Despite the prurience of the format and the annoying presenter who tried to inject drama into EVERY! SINGLE! SENTENCE! it did reveal a fascinating truth. When Jill filled out a food diary for the week, her average daily calorie intake came to about 1300 calories. But when you totted up what she actually ate, as revealed by all the hidden cameras, the real figure was something like 3000 calories a day. Her mystery 5-stone weight gain isn’t such a mystery after all.

The bigger point is this: many, many studies of what people eat rely on participants filling in food diaries. This is an astonishingly inaccurate way of collecting data, as Jill’s experience shows. First, people forget what they eat very quickly, and second, we always under-report the bad stuff, over-emphasise the good stuff, or simply lie. The very fact you are taking part in a study probably influences what you eat as well.  Any conclusions based on data gathered like this, such as the baby weaning study I wrote about a few months ago, must be treated with so much caution as to be virtually meaningless.

I can see why researchers use food diaries: it is very difficult to gather accurate information about what people really eat (unless you are Channel 4 and use secret cameras and PIs). They don’t have many other tools at their disposal – shadowing your subject 24/7 isn’t really an option. That’s why prisons and schools are so useful for dietary experiments, as you have so much more control over what food your subjects have access to.

I wonder if this is why you get so many contradictory headlines about diets – particularly of the ‘red meat/wine/coffee will kill you/make you live forever’ variety. If the data used in these studies is so flawed, it’s really not surprising you can draw any conclusion you like from it.

I am a great fan of Pret a Manger. As Mary Portas said in her recent review of high street chains, their coffee is consistently the best and the staff are always fast and friendly. They were also amongst the first to switch to organic milk (Rachel’s) and Fairtrade coffee. And the Notting Hill Gate branch was very cramped. It is our regular pit-stop after the market on a Saturday morning, and there were never enough seats. Portobello-bound tourists lingering long over their guidebooks got the hairy eyeballs from impatient regulars like me waiting for seats.

But but but. On Notting Hill Gate, from memory, I can recall 2 (perhaps 3) Starbucks, EAT, Pret a Manger, Cafe Nero, Apostrophe, Le Pain Quotidien, and one or two independents. There’s also an Itsu, McDonald’s, KFC, Nandos, Pizza Express, Frae, and a few fried chicken / kebab shops. It’s wall-to-wall coffee, takeaways and fast food, of varying quality, from one end to the other. This isn’t a high street, it’s a food court. It’s what I would expect to find in an airport, albeit a windy one with buses driving through the middle of it.

In the most recent edition of Fire and Knives, Ralph Bullivant writes about his Saturday morning shopping rituals in Birkenhead. He goes to a fruit and veg shop run by two Iranian brothers, the original Birkenhead Market for the fish stalls, an Asian supermarket and a sixth-generation butcher that has been in business since 1844. In doing so, he tells us a lot about Birkenhead, its past, its decline and its current residents. A trip to the supermarket may have been easier, quicker and possibly cheaper (though not always). But it would offer no connection to the people, places and history of Birkenhead, and all the richness that brings.

If we lose all our food shops, particularly the smaller, independent ones, we lose much more than a place to buy our food. We lose fragile threads that connect us to our neighbours, our past, our culture, our sense of belonging. We all become alienated travellers, gliding past identikit outlets, using brands and logos to navigate our way through new yet always familiar landscapes.

It’s not all doom and gloom, however. Two weeks ago, with much excitement, Christchurch Fish arrived in the Notting Hill Farmers Market, an event I had been looking forward to for weeks. There were ugly scenes as fish-mad shoppers converged on the stall soon after 9am. I think they were a bit overwhelmed: they didn’t have their filleting station set up and the traffic warden was trying to ticket their van. I bought two mackerel for £3 and the man forgot to both take my money and hand me my fish. But the fish was good: huge crates of fresh blue lobster and brown crabs, bream and mackerel and sole. We’re going back for more this week.

Take food, for example (how did you know that was coming?). Food can be good and cheap, but takes time (shopping, preparation, cooking). Food can be cheap and quick, but not good (fried chicken, chips and cheap burgers). Food can be good and quick, but therefore expensive (decent restaurants, fillet steak etc).

I used to think ‘cheap’ food was bad, but now I think it’s not the cheapness that defines it. There is cheap good (lentils, vegetables, cheaper cuts of meat) and cheap bad (highly processed food, Turkey Twizzlers, mechanically recovered beef). The difference isn’t money, it’s approach: making cheap food good takes time, planning and a degree of skill, and that requires education.

So it’s nice to see Jamie Oliver and Steven Gerrard front a letter to the PM calling for better food and cookery education in schools. How depressing that food is only currently taught as part of the design and technology curriculum. I’ve heard stories that a typical lesson might involve designing a new take-away pizza box (I’m not sure if this is actually true, but it sounds horribly plausible).

It’s also a bit depressing, if you read to the bottom of the story, that the government defends itself partly by pointing to the Responsibility Deals it has set up with food manufacturers. As I wrote back in February, I hope they’ve put some evaluation criteria in place for this scheme, because it doesn’t seem be the most obvious solution.

How marvellous it would be to be proved wrong.

I think this is really interesting, and has implications for the wider healthy eating debate. Basically, people don’t have the willpower to choose the good stuff when the bad stuff is also available. The best (only?) way to prevent them choosing bad stuff is not to offer it at all. I think the behavioural economists call it choice-editing, but a more old-fashioned term would be regulation.

So: regulation works, free choice doesn’t. I don’t think the Health Secretary would like that one bit.

Consider this:

Sunday – roast
Monday – cold meat
Tuesday – mince
Wednesday – soup
Thursday – freestyle
Friday – fish
Saturday – freestyle

And back to Sunday again. Someone mentioned this list at the weekend, and I’ve read it somewhere, and when I can be bothered I will look up the reference. It is possibly a generational thing; usually it is older people who remember or still use such a plan. Also, to an older generation, fish on Fridays was a given, a tradition we have largely lost.

My point is that this plan is almost always mentioned in a derogatory way. How awful! Having to eek out the joint for three or four days till there’s nothing left but watery soup. Thank god for teriyaki salmon, thai green curry and takeaways pizzas.

Except, of course, there is more to it than that. Depending on the skill of the cook, and the quality of the ingredients, there is no reason why this plan couldn’t give you several entirely delicious meals. It’s economical and, most importantly, it saves the cook from having to think too much. If you have a basic pattern (albeit one that can accommodate lots of variety) it makes planning, shopping and cooking much simpler.

What would a modern weekly round look like?

My mother would be very cross if I didn’t mention that it was her who spotted it and took the photo.

Actually, scratch that, I’m delighted. As they have aggressively expanded into almost every area of UK (and now global) retail, they seem to have pissed off a huge number of customers, suppliers (especially in the food sector) and people in towns where they have opened shops despite local opposition. They have no cushion of goodwill or brand loyalty to fall back on. They’re not even that cheap anymore, now Lidl and Aldi have arrived.

I suppose all big businesses and sectors go through cycles, and Tesco is no different. Having had a few years in the sun, their rivals have started to catch up and now overtake them. The problem is that the massive expansion of Tesco (and other supermarkets) has hollowed out the food retail sector. Smaller shops and producers with shallower pockets are less able to ride out the bad years, and huge numbers of them have shut down in the last decade.

If Tesco’s current investment programme doesn’t turn the stores around, presumably the next step will be for them to contract and close the less profitable stores. Perhaps this will be an opportunity for smaller players to open up again? The laws of free market economics would predict this. Yet I suspect successful small shops take many years to establish themselves and build up a regular clientele, lacking the advantages and profile conferred by a national brand. And if the small shops don’t spring back once the supermarket withdraws, we’re going to end up with a lot more food deserts. Surely we can do better than that?

In Jerez, the streets are planted with orange trees for decoration, the equivalent of our municipal beds of clashing geraniums. The last of the oranges are on the trees now and, as they fall on to the pavements, the children use them for practising their football skills. Only English visitors scurry about collecting unblemished specimens to turn into marmalade, a habit the Jerezanas entirely lack.

There is a brief lull in the Jerez calendar at the moment. Semana Santa (Holy Week) has just finished, and in the main plaza they are still dismantling the stands that were used to watch the various processions go by. In a few weeks it will be Feria, the gypsy festival of horses and flamenco, eating and drinking. We saw a vast acreage of tents being erected on the outskirts of town in preparation.

I gazed with longing and wonder, not for the first time, at the beautiful Eiffel-designed fish market in the centre of town. This city, with about 200,000 inhabitants, supports a market with around 40 separate fishmongers. Some had specialities – hake, or tuna, or sardines, for example – but many sold a bit of everything. We bought prawns, small clams, dogfish and cuttlefish for a seafood rice. The fishmongers were complaining that trade was down because the bus service into the Plaza had stopped running. The city of Jerez is, apparently, 1bn Euros in debt. Teams of economists and documentary makers from all over the world come to Jerez to study the southern European debt crisis – just how do you rack up a debt of 1bn Euros? But the upshot is the bus drivers and the cleaning ladies haven’t been paid, so they have gone on strike. The man who sold us the dogfish said the good news was the bus drivers had all been sacked (so that’s alright then) and new ones recruited, so the buses should be running again soon. But how will they be paid?

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