Bob Crow, general secretary of the Rail Maritime and Transport union (RMT) said problems on First Great Western (FGW) services following the introduction this week of the winter timetable proved the rail franchising system "simply cannot deliver the railway we need".

Mr Crow gave his backing to an Early Day Motion criticising FGW. It was tabled by Stroud Labour MP David Drew and has been signed by 19 other MPs.

The motion calls on the Government to consider bringing the Greater Western franchise, which has run by FGW since it was launched in April 2006, into public ownership.

Only East Coast Main Line operator GNER has a poorer punctuality record than FGW, which ran only 83 per cent of trains on time during the summer, compared with a national average of 90.8 per cent.

Mr Crow said: "Since the timetable changeover, there have been more delays and serious overcrowding on commuter trains in and out of Bristol and, as usual, it is our members who are left to pick up the pieces and face the public's anger."

A spokesman for FGW said: "We are investing £200 million in trains, stations and customer services. Our high-speed train fleet which serves Mr Drew's Gloucestershire area has been fitted with new engines and new interiors to enhance safety, comfort, capacity and reliability in a major refresh programme.

"Our local trains which serve Gloucestershire, is also being upgraded in a multi-million pound project and have begun to enter service." On Wednesday, FGW's managing director Andrew Haines admitted the firm had experienced teething problems with the new timetable.

But he insisted issues of overcrowding, delays and cancellations of services had stemmed from problems beyond the operator's control.

Mr Haines apologised to customers who, in some cases, have been unable to get on to trains or hit by delays and disruption since last Monday.

In the early part of last week, Bristol Temple Meads and stations in North Somerset and the Bath saw a repeat of last year's chaotic scenes which eventually led to a protest group organising a fares boycott.

Passengers complained last week of a shortage of carriages on some services and spoke of fears about a limited number of doors being available to open on long distance trains that now stopped at small stations.

Yesterday, FGW spokesman Lance Cole said major improvements had been seen during Thursday and on Friday morning as a result of switching carriages on to busier services to meet demand.

Mr Cole added that early problems with selective door opening on high speed services calling at local stations had been ironed out.

Recent changes have included reducing the normal two-carriage 5.49pm Temple Meads to Severn Beach rush-hour commuter service to one carriage to free capacity for busier routes.

The Government plans to make 1,300 extra carriages available over the next seven years and Mr Cole said FGW would lobby as hard as it could to ensure the company was allocated a share.

David Redgewell, of lobby group Campaign for Better Transport, said he had seen in improvement in services run by FGW during the latter stages of the week. But he urged the Government to work with the train company to make extra carriages available.

This weekend, FGW is using a hired old-fashioned locomotive and coaches between Bristol and Chippenham to help provide extra seats. Mr Redgewell said he hoped the extra train could also be used to ease overcrowding on weekday commuter services.

Although there were no plans to use the hired train through the week, Mr Cole said the idea should not be ruled out completely.