Rail operator First Great Western has promised to make more changes to its timetable after being confronted with a dossier of complaints by passengers from Oxfordshire.

The rail operator made the pledge as part of a 40-point action plan outlined to MPs this week but was not yet able to confirm details of alterations - some due to come into effect in May.

The announcement follows a showdown meeting between Oxfordshire MPs and Transport Secretary Douglas Alexander on Wednesday night to discuss the catalogue of problems for passengers since FGW changed its timetable last December.

Key Oxford and Didcot commuter services were cut, but FGW was forced to reinstate some trains in January following a public outcry.

The firm's service over the past three months was branded as shambolic in a report compiled by commuter group Ox Rail Action, which has been sent to FGW, MPs and the Department for Transport.

Another round of timetable changes will take place in December. FGW's recovery plan also includes its previously-announced £160m programme to re-engine its InterCity 125 High Speed Trains and refurbish their coaches, to increase reliability and seating capacity.

The overhaul programme is due to be completed by December, allowing smaller Adelante trains to be removed from service.

FGW spokesman Adrian Ruck said: "We're confident that this investment will make a huge difference to the performance of our services in terms of reliability and level of comfort that customers expect."

He added there would be no specific consultation on the May timetable changes.

Mr Ruck said: "The changes are the result of consultation, customer feedback and dialogue with MPs."

But Oxford East MP Andrew Smith, who handed a copy of the Ox Rail Action report to Mr Alexander at the meeting on Wednesday, said commuters should be allowed to comment on the planned changes.

"It's important we all keep pressing until we get decisive improvements in services. I'm demanding proper consultation with passengers before the May timetable is drawn up," he said.

"I stressed to the Secretary of State the importance of action to improve the quality of services and carriages to tackle overcrowding, as well as the need to improve punctuality.

"First Great Western are making huge profits and they need to get their act together to give Oxford rail travellers the services they need and deserve, and which they are paying a lot for."

Wantage MP Ed Vaizey, who was bombarded with complaints from constituents, welcomed moves to change the timetable. But he said he would be maintaining pressure on the rail industry to make all-round improvements in services.

Ox Rail Action spokesman Zahra Akkerhuys said: "We're pleased that local MPs are joining us to keep this issue at the top of the agenda. Oxford services have to improve, not just for passengers, but also for the health of the Oxford economy. This is not a campaign that will not go away."