In the red corner... the Aslef chief and a barbecue that was too hot to handle

It was meant to be a jocular knees-up for officials of the train drivers' union and their staff. The venue was a garden next to the union's head office - a sumptuous mansion in Hampstead, north London, that was once home to the conductor Sir Thomas Beecham.

But the barbecue at the headquarters of Aslef, one of Britain's most macho unions, ended in discord - with a midnight brawl among large middle-aged men.

And today, the ramifications of that violence could lead to the suspension of at least three of the most senior officials. Among them is likely to be Shaun Brady, 41, the general secretary and one of Tony Blair's few remaining allies in the union movement.

Martin Samways, Aslef's left-wing president, and Mick Blackburn, assistant general secretary and a Brady ally, are set to be the subject of similar disciplinary procedures at the hands of the executive council.

The fracas is understood to have resulted in Mr Samways "getting a good kicking" and Julie Atkinson, Mr Brady's assistant, being "laid out".

The all-powerful committee, dominated by the left, will receive an initial report today on the unfortunate goings-on from the vice-president and the union's legal officer. It is expected that the executive will then suspend the main dramatis personae and call for a full inquiry led by an independent outsider.

The punch-up took place last Thursday night as the rest of the nation looked forward to a few days of sunny weather and an ideal weekend for barbecues.

Overlooking the venue is the home of the actor Richard Wilson. In character as Victor Meldrew, he might have been tempted to remark that he did not believe what was going on if he had witnessed it. But the union, one of the country's most powerful, has been riven with internal conflict since Mr Brady, a right-winger, was elected last July and, as one source said: "You could see this coming. It's amazing it hasn't happened before."

There are as many versions of what took place at the "battle of the barbecue" as there were participants and onlookers. One version has Mr Samways leaving his bed in a flat he occupies on the site to complain about a party-goer who was making disparaging remarks at full volume about the union's left-wingers. Another has the general secretary taking issue with the unacceptable behaviour of the president who allegedly turned up late and uninvited at the party.

A spokesman for Aslef said that a number of the union's employees had complained about Mr Samways' conduct and that the executive council would consider the issue today. But statements made by other onlookers make allegations against the general secretary.

Last July, much to the surprise of outsiders, Mr Brady, a former driver at South West Trains, was elected general secretary in succession to the left-winger Mick Rix.

On his election, the new union leader vowed to "take the union back to the membership". He promised to put pay and conditions at the top of his agenda, avoid political campaigns involving issues outside the industry and keep his differences with Labour Party policy private.

Importantly he enjoyed the backing of Lew Adams, a former leader of the union, who is now a member of the Strategic Rail Authority.

The identification of Mr Rix with left-wing causes such as the opposition to the war in Iraq and support for Cuba may have detracted from his popularity with the membership. Train drivers are proud of their craft and not necessarily among nature's radicals.

But it was thought that Mr Brady's success would do little to foster harmony among unions in the industry. He once traded blows with Bob Crow, the left-wing leader of RMT, the industry's biggest union, while the two men were on a delegation to Eastern Europe. To this day there is an uneasy relationship between the two men.

Last month Mr Brady complained that the Old Labour executive had stripped him of most of his powers and that he was unable to buy so much as an extra jar of Nescafé without its say-so. He said he felt "under house arrest" and had less clout than the office cleaner.

The move by the executive followed his opposition to a decision to initiate an inquiry by Matthias Kelly QC into the alleged misuse of union funds during the past 10 years. Mr Brady argued that the investigation would be an expensive waste of the members' money. The TUC intervened in January after Mr Brady threatened to hire "scabs" to replace the union's administrative staff who were threatening to walk out.

Aslef itself has been responsible for a series of strikes on the railways which has resulted in a substantial increase in train drivers' pay. And whatever the outcome of any inquiry into the fracas, the reputation for machismo enjoyed by Aslef's senior officers will be inevitably be enhanced by the brawl at the barbecue.

The union has tried in recent years to alter its male-dominated image and ensure more female trainees are attracted to the footplate. But the latest figures show that there are 15,670 male members and only 502 women. The sight of a female delegate to the annual conferences of the union - full name, the Associated Society of Locomotive Engineers and Firemen - is a rarity indeed.

One former senior official at Aslef was asked why there were not more women train drivers. He replied that if more were recruited, they would have to start putting basins in the cab so that they could do the washing up. No one was entirely sure whether he was joking.