So who are our spies snooping on today?

When William Waldegrave, a former Foreign Office minister, spoke yesterday of "tapes of what some foreign leader said in his bath", he wasn't joking.

Britain's Secret Intelligence Service, MI6, would not hesitate to try to listen in on any conversation, intercept any mail or hack into any computer if it would give the country an edge over our competitors - even if they happen to be our friends.

Intelligence experts were staggered yesterday that anyone should be at all surprised at MI6 conducting secret operations against Britain's European Union partners.

"That's its job," said Nigel West, an intelligence historian. "The Secret Intelligence Service costs pounds 900m a year and if it couldn't assist ministers in finding out what other states are up to, then it wouldn't be worth the money."

The targets in modern-day espionage, aside from drug trafficking and money laundering, are primarily political and economic rather than military. If a British minister has to enter negotiations with other countries, he wants to know what their positions will be before he enters the room.

If that means bugging the home of a senior foreign official or an EU commissioner, then, with ministerial permission, its operatives will do it.

They recruit contacts inside government departments and, using Britain's electronic listening station GCHQ, they pick up whatever conversations they can.

During the Seventies, in advance of a round of talks on the sovereignty of Gibraltar, a bug was found inside the private office of the Spanish prime minister. It is thought to have been put there by a British spy.

"Intelligence gathering does not have to be hostile and it can sometimes be to the benefit of the country being observed," said Mr West.

"If we intercepted something which showed, for example, that French communication systems were not secure, then France would be grateful. But we have to listen in to make sure they are safe; there's no point us sharing highly sensitive information with them if they're going to let it out. The process is controlled by the Joint Intelligence Committee, but a clandestine electronic eavesdropping operation would require personal approval from the Foreign Secretary.

An intelligence source, who asked not to be named, said: "The minister would have to weigh the value of the information that might be gleaned against the potential embarrassment of being caught.

"But the other countries do it to us, too. It's all part of the game and the rewards for the winner can be immeasurable."