The results will be used to determine whether key staff at contractors are suited to working with the rail operator on major projects.

Network Rail's director of infrastructure and investment Simon Kirby said: "We are looking more and more at people's behaviours and how they operate. It's more important than the price of a job."

Bidders for the delivery partner role for the £550 million revamp of Birmingham's New Street station have already attended day-long assessments that have also included team-building exercises and interviews with Network Rail.

The rail operator also wants to ensure that the people assessed are actually those that will be working on the job.

One of the contractors who attended said: "They're trying to make sure they get the right team on board - that can only be a good thing. But sometimes they can end up with too much information and get confused about who should get the job."

Contractors usually spend three to four weeks preparing bids for large Network Rail jobs and the process is already an expensive one. There are fears that additional assessment could delay the tender process.

But Network Rail is sticking to the idea and plans on using psychometric testing on contractors bidding on the £3.5 billion Thameslink jobs as well as future framework agreements.

Mr Kirby said: "These are long-term projects and it's more down to people and behaviours rather than the bid proposal."

In future contractors will also be given more of a heads-up before future projects are put out to tender.

Network Rail wants suppliers to have a better understanding of what is required ahead of a job being advertised.

What is a psychometric test?

A psychometric test is a way of assessing a person's ability or personality in a measured and structured way.

There are two main types of tests and these look at ability and personality.

Ability tests examine numerical and verbal reasoning.

Personality assessments require candidates to answer multiple-choice questions on how they perceive themselves.

Analysis: Network Rail needs clear targets

By Lea Brindle

Users of psychometric testing need to be clear what characteristics they are seeking. For instance, being an organised team player might be considered a positive quality for successful contractors.

A psychometric personality test can assess these characteristics more quickly and more accurately than the average manager.

But Network Rail needs to be aware there are dangers.

For instance, how organised must a contractor be? If highly organised, they may be too inflexible. If too team-centred, they may be just a "yeah sayer" leaving everyone happy but contributing nothing.

Apart from psychometrics, assessors often use structured exercises to assess problem-solving, team playing or influencing skills. These exercises often fail because of the lack of proper training of assessors.

Contractors can help by being clear about their key skills and personal qualities and having confidence that these will be assets to the organisation, even if contrary to the managers' initial views.

Dr Lea Brindle is a chartered occupational psychologist and runs Value Added Business Psychology