Aslef's general secretary Shaun Brady has been suspended

The drivers demanded to see members of the union's executive, but were denied access to the building.

They had earlier met in a nearby pub, where they were addressed by Aslef's general secretary Shaun Brady.

Mr Brady and two other senior officers were suspended after an alleged brawl at a barbecue at the Hampstead headquarters on 20 May.

Two investigations

The drivers had gathered to back Mr Brady and voice opposition to the union's executive.

The protest's organiser, Steve Strumm, 42, said the cause of the unrest was not the "battle of the barbecue" but the state of Aslef's finances.

"We are told the union has a �900,000 deficit but we are also told that last year there was a �500,000 surplus, so where has that money gone?" he said.

WHAT IS ASLEF? Aslef is the principal trade union for train drivers It was founded in 1880 for drivers and train crew It has about 17,000 members working on trains, London Underground and trams Aslef is affiliated to the Trades Union Congress and Labour Party

"We are demanding that the executive publish the accounts and tell us what has happened."

The union is awaiting the results of separate investigations into its finances and the alleged brawl.

The train drivers' protest came on the day that they were due to attend their annual conference, which was postponed while an independent panel examined the barbecue allegations.

The three-person panel is expected to report to the union's executive shortly.

Since Mr Brady came to power nearly nine months ago, he has had a strained relationship with supporters of the previous leader, left-winger Mick Rix.

'Warts and all'

One union source had told BBC labour correspondent Stephen Cape he hoped there would be a "grassroots protest" with a possible demonstration outside the union's head offices.

But a member of the executive said disciplinary action may be taken against anyone who broke Aslef rules.

He urged members to wait for publication of the reports, which he said would reveal the truth, "warts and all".

Following the alleged brawl, assistant general secretary Mick Blackburn and president Martin Samways were suspended along with Mr Brady.

Mr Brady, 41, elected to his post last July, is seen as a Blairite and has differences with members of the more left-wing executive committee, of which Mr Samways, 57, is a member.

He has complained of losing day-to-day control of the union because of arguments with the executive and his concerns have led to an investigation of the union's finances over the past decade.