Last week was our best week for the past 50 weeks

Mike Carroll, First Great Western

Christopher Irwin, chairman of the Western England Rail Passengers Committee, said: "First Great Western has been the subject of enormous number of complaints over the last period.

"It's done very badly in terms of reliability.

"For example, on punctuality something like only just over half of trains arrive within ten minutes of the right time."

Passengers' evidence

First Great Western has complained that the investigation has been called just as services are improving.

Spokesman Mike Carroll said: "Last week was our best week for the past 50 weeks

New trains are due to go into service

"And we don't think it will add anything to improve the performance of First Great Western."

The inquiry is being conducted by the Rail Passengers Committees for London and the South West.

Passengers are being asked to give evidence about their own experiences.

In July, the company unveiled an �80m fleet of new passenger trains at a ceremony in Bristol.

They have been built to run between Bristol and London.

But the first new train has yet to run - nearly a year after it should have gone into service.

'Desperate time'

Technical problems have led to delays.

The company said the new trains would allow more frequent services and would lead to dramatic improvements in performance.

At the time of the launch, chief executive Moir Lockhead said: "Commuters on the railway between Bristol and London have had a desperate time over the last three months."

Train numbers between London, Bristol and Cardiff had been increased, he said.

Rail Passengers Committees were set up by parliament to protect rail users' interests with powers to recommend changes.