Big improvements to the way the rail network is maintained have been promised by Transport Secretary Stephen Byers.

He was speaking to the annual conference of the train drivers' union Aslef 10 days after the derailment at Potters Bar which killed seven people.

It's safety that has to be paramount, not the lowest price which is put forward

Stephen Byers

Mr Byers said it was too soon to judge what happened to the points at Potters Bar, but now was the time to look at the role of contractors and sub-contractors who work on railway maintenance.

On Monday trains began running again through the Hertfordshire station as the firm in charge of the line said photographs backed its claim that sabotage caused the crash.

Best value approach

Jarvis said photos taken immediately after the accident showed that as well as two sets of nuts being removed from the points, an inner set of nuts had been adjusted in the 48 hours before the crash.

The company's statement added: "No maintenance had been carried out on the points in the previous 48 hours."

Mr Byers said the future relationship between rail networks and contractors must be based on "best value" and not the "lowest cost put forward".

The transport secretary said he was responding to concerns raised by railway unions, the Commons transport select committee and the Cullen report.

Stephen Byers: Concerns over contractors

Lord Cullen also made some very specific recommendations in relation to the use of contractors.

'Real progress' expected

He called for improvements to the selection process of contractors and better checks on their work.

Mr Byers said he had written to the Health and Safety Executive on 1 May asking for a report on action being taken to implement the Cullen recommendations as they applied to contractors.

Trains began going through Potters Bar again on Monday

He said: "Come the end of the month, I will expect real progress to have been made and a clear timetable of the full implementation of the Cullen recommendations as far as contractors are concerned.

"We need to go further and look at the role of contractors and sub contractors, both in terms of running a safe railway system, but also one that is more reliable because work is done on time and to schedule."

Mr Byers said John Armitt, chief executive of Railtrack, had recognised "changes need to take place".

Skills and training

Any new relationship had to implement the Cullen recommendations, he said, but also needed to change the way contractors and the network operated.

He said: "This can come about through longer contracts, insistence on skills and training, an alignment of incentives and perhaps most importantly, by awarding contracts on the basis of a best value assessment and not simply the lowest cost put forward.

"It's quality. It's best value. It's safety that has to be paramount, not the lowest price which is put forward."

Network Rail, which is likely to be the successor to Railtrack, would need to treat as "top priority" changes to its maintenance and track renewal programme.

Rail academy

"Not because of what the conclusions might be from Potters Bar, but because of the concerns that have already been expressed about the role of contractors and sub-contractors," said Mr Byers.

The transport secretary welcomed the establishment of a national rail academy which would focus specifically on the needs of the railway industry.

Gwyneth Dunwoody, who chaired the Commons transport select committee, agreed the measures mentioned by Mr Byers were needed.

But she said: "The real problem is that Railtrack itself needs engineers and it needs people in house who can actually check what's being done in its name."

Mrs Dunwoody told BBC Radio 4's World At One Mr Armitt was keen to act but the impact of just making the maintenance contracts longer was "debatable".