The coffee-chain cappuccino is an excellent barometer of pricing, since it is, unlike a salad or a plate of spaghetti, a uniform product. The Economist magazine has taken advantage of this fact by constructing a "Starbucks tall-latte index" to check currency valuations, but budget constraints for the humble Undercover Economist meant that my own investigations took me no further than Watford Gap.

Watford Gap is the oldest motorway service area (MSA) in the country. After a long wait in the queue there, I purchased a Costa Coffee cappuccino - which, apart from being 10 per cent more expensive, was identical to the high-street product in all respects - and something called a "ham and three cheese tostato", which was quite disgusting and carried nearly the same premium. Most travellers will recognise the distinctive motorway experience of high prices and low quality, but they may not know who is to blame. Underneath the elevator music and sad Formica tables for the single traveller lies a remarkable government campaign, as old as Watford Gap itself, to make MSAs as grim as possible.