If the fleas are in the cabs, then they could conceivably get into the carriages too

Lorna Willard Thompsons solicitors

"The fleas have been found in drivers' seats in a number of trains. The warm cabs are an ideal breeding ground," said an Aslef official.

"We have asked managers to fumigate the cabs but they just turn up with a tin of fly spray every now and then, which is obviously not good enough."

He said drivers had been complaining for months about the fleas but say they were only taken seriously when one of the insects was caught and shown to a manager.

Lorna Willard, from solicitors company Thompsons, which helped secure compensation in a recent case, said: "I suspect the travelling public would not be too keen to hear that underground trains appear to have a problem with fleas.

"If the fleas are in the cabs, then they could conceivably get into the carriages too.

'Not a problem'

"London Underground really must act to clean up their trains."

London Underground said it had dealt with only one flea-related claim for compensation in the past year but a spokeswoman said any complaints would be followed up.

"We don't regularly spray trains because we don't believe it is a problem, although we will obviously deal with any cases which are drawn to our attention," she said.