Which? Magazine’s researchers (issue of June 25) found that “Smedleys Atlantic Prawn Marie Rose Salad, £1.49 (300g) - available at Morrisons - contains 855 calories and 66.3g fat - more than a McDonald's Big Mac and medium fries and 70% of the fat a man should eat in a day” and nearly the entire recommended daily fat intake for a woman of 70g.

The real problem with prepared and convenience salads is, unsurprisingly, a lack of uniform, accurate and genuinely informative labelling on these supermarket and convenience store chiller-counter products. Usually the surprise calorie-villain was a dressing made of mayonnaise or something equally creamy in texture. For example, it was “the second highest ingredient (27%) in an M&S Pasta with Tomato & Basil Chicken salad, £3.20 (380g), which had 760 calories and 46g fat.” But somehow worse was Sainsbury’s Tomato & Basil Chicken salad, £2.95 (350g). “The label,” says Which?, “specified that it had no mayo but the ingredients list revealed that it contained egg yolk, oil and white wine vinegar - the same ingredients as mayonnaise.”

Another unhelpful label was on Tesco’s Tuna Layered Salad. It appears that it has 275 calories and 20.5g fat - but this is for only half the pack. If you ate the whole 350g pack, which is a perfectly sensible quantity for one person, you’d be taking in 550 calories and 41g fat.

Obviously my best advice to anyone watching his calorie intake would be to prepare your lunchtime salad at home, where you can use lovely crunchy, crisp salad greens and ripe, perfumed tomatoes;  control what goes into the dressing; and, indeed, make sure you use healthy olive oil. But let’s be realistic: sometimes you just have to snatch something from Tesco Metro or M&S Food. What can you do?

• Try to buy pre-packed salads where the dressing comes in a separate packet – then you can either discard it or use only a little of it (or dress your salad with a squeeze of lemon, a dash of soy sauce or the tiny bottles of olive oil and red wine vinegar you always keep in your desk drawer!)
• Another good tip is to choose salads that favour protein over carbohydrates – salade niçoise, for example, or a salad with meat. poultry, fish or prawns instead of one with mostly potatoes, rice or pasta; bean salads are better, too.
• And when you look at the ingredients, remember: egg yolk + oil + vinegar often = mayo.