By Tom Symonds BBC transport correspondent

The increased use of outside engineering companies to do work on the tracks hardly affects passengers, and isn't obvious to passengers but it has become a controversial issue, and even more so following the Potters Bar train crash.

At the centre of the debate is Railtrack - a company which has engineering at its heart, and a duty to maintain the health of the rail network.

Yet Railtrack does not employ many people who actually get their hands dirty.

In fact, for a long time there was hardly an engineer to be found within the company's boardroom.

The crashes at Hatfield and Potters Bar were both caused by faulty track which was maintained by private contractors

Railtrack contracts out the work of inspecting, maintaining and replacing track to a range of engineering firms.

The biggest are Jarvis, Balfour Beatty, Carillion and Amey.

They in turn might contract out work to smaller companies which put together gangs of track workers.

Even these companies might not directly recruit their workers - often they are provided by specialised recruitment agencies.

This complicated string of arrangements has been regularly criticised by the Transport Select Committee, which regards the use of contractors as one of the biggest problems caused by privatisation.

The crashes at Hatfield and Potters Bar were both caused by faulty track which was maintained by private contractors.

Raising standards

Newspaper reports have claimed that track workers break the safety rules by doing double shifts to earn extra money and that they're more interested in getting home early than getting the job done.

Railtrack has begun a full investigation.

A report by the Health and Safety executive this week accepts that contracting out work does not in itself result in poor safety standards.

Others might disagree, but the Health and Safety Executive (HSE) does raise concerns about the commitment of the rail industry in general and Railtrack in particular, to tighten up standards.

The report calls for "commitment and leadership from senior managers in the industry to ensure words on paper become reality".

It will require an "acknowledgement of responsibility by Railtrack".

The HSE was not impressed at the number of occasions that Railtrack opposed attempts by inspectors to improve safety standards.

Another big concern is the lack of any system to ensure that work done on the track is properly carried out.

Staff training has so far been left to the contracting companies.

But Railtrack is now developing plans for training track workers.

Railway reform

It is also trying to sign more long-term contracts, to ensure good staff are kept in a job.

The HSE says "it is arguable that this should have happened sooner".

Railtrack is ultimately responsible for work done on its railway lines.

However, the HSE has powers to prosecute when things go wrong.

Railtrack will lose its role as custodian of railways

It is currently carrying out an inquiry into the death of a student, Michael Mungovan, while working on business rail lines near Waterloo station in south London.

He was hit by a train.

The verdict of an inquiry jury was that he was unlawfully killed.

It is clear that the rail industry is under pressure to tighten up the system of contractors.

Before he resigned as Transport Secretary, Stephen Byers, said just "tinkering at the edges" was not enough - a complete reform of the system was needed.

Soon Railtrack will be taken over as the custodian of the nation's rail lines.

It will be replaced most likely by a government backed consortium called Network Rail.

The question is whether this newcomer will decide that if you want a job done, it's worth doing it yourself.