Alan Woods, chief executive of Keep Britain Tidy, said: "After closing time, many revellers simply can't find a loo to use."

A campaigner said London's street cleaners were dealing with two million pints of urine a year.

The problems were partly being blamed on councils closing conveniences.

Bucking the national trend is Westminster Council, which has to cater for more than one million visitors a day to the UK's tourist and entertainment hub.

It spends �2.6m a year on public toilets and has 30 facilities - more than it has had at any time in the last 20 years.

'Disgusting sight'

Delegates at the conference, partly organised by the Keep Britain Tidy group and the British Toilet Association, are debating whether authorities could charge more for the use of public conveniences.

Research carried out showed 95% of people surveyed had admitted to urinating, vomiting or defecating in the streets.

"While it is a disgusting sight to see - and a joyless job to clean up - public pee-ers have little option. Too many conveniences have either been shut or appear dirty, shady or dangerous," Mr Woods said.

Judith West, chairwoman of the British Cleaning Council, said: "Aside from removing a tide of trash from our town every day, street sweepers clean up two million pints of urine from the streets of London per year.

"What a thankless task that is. We should be investing more in public loos and encourage businesses that are making a fortune from extra licensing hours to put their hand in their pocket and pay for more conveniences."