Tormented by nutritionists who worry about expanding waistlines and shareholders who fret about flattening sales, the fast-food chain is launching its biggest menu revolution in 30 years and making a grab for the £445 million-a-year prepared salad market.

By the end of this month, customers at the 1,235 McDonald’s restaurants will be offered the choice of adorning their grilled chicken salad with Caesar dressing (and croutons) or the lighter option of a drizzle of balsamic dressing.

However, anyone hoping that salad is the slimming option should read the nutritional information on the McDonald’s website, which reveals that simply switching from burger to salad will not help to shed the pounds.

A chicken Caesar salad with dressing and croutons contains 425 calories and 21.4g of fat, compared with 253 calories and 7.7g of fat in a standard hamburger. Add a portion of fries to your burger and the calorie count climbs to 459, but is still less fatty than the salad at 16.7g.

McDonald’s said that without the creamy sauce and croutons, the fat falls away — but so does the taste, unless you opt for balsamic (73 calories and 2g of fat).

Free of dressing, a McDonald’s chicken Caesar has only 222 calories but still has more fat than the burger. “It’s the Italian cheese,” explained a spokeswoman. The salad also costs more, £3.49, compared with £3.20 for a Big Mac.

Andrew Taylor, the chief executive of McDonald’s in the UK, admits that alarm over obesity in children has played a part in converting McDonald’s to greenery. “It is a significant issue,” he says. But the big problem facing McDonald’s has been boredom with burgers. Between 1998 and 2003, sales growth in the US was barely 1 per cent per annum.

Tests with British consumers show a fifth of customers would buy one of the new salads and more than 90 per cent would come back for more. Mr Taylor did his own taste test yesterday in a restaurant in the Strand, Central London. One customer, tucking into cheeseburger and chips, turned down a free salad — “I don’t like salad” — but another couple, Bob Waldron and his wife, agreed to sample the new product.

The verdict was positive and Mr Waldron said he would have it again if he were in McDonald’s with his children, but he added: “I wouldn’t go to McDonald’s for a salad.”

Times Recommends

• Olympic-size television coming to your town
• Mosley opens new front in battle for privacy
• On-the-spot fine for man smoking in his van