Outside threat to Network Rail veteran's tilt at the crown

'Strong' car-industry candidate casts doubt over Simon Kirby's bid to replace Sir David Higgins as chief executive

Network Rail veteran Simon Kirby faces an uphill struggle to take the top job at the state-backed track and station operator, as an external candidate is said to have emerged as a heavy favourite.

It is understood that Mr Kirby, who joined Network Rail 10 years ago and has sat on the board since 2008, has moved ahead of fellow director Robin Gisby as the leading internal candidate.

The former BAE Systems exec, who is currently in charge of large infrastructure projects, was recently interviewed to replace outgoing chief executive Sir David Higgins.

The rail industry was shocked by news this summer that Sir David, who was knighted for overseeing the construction of the much-lauded London 2012 Olympic Park, was quitting next year.

This was earlier than most industry insiders had expected and was revealed shortly after the Australian was heavily criticised for getting a £99,000 bonus when Network Rail had missed some of its performance targets. He leaves at a crucial time for Network Rail, as it comes under pressure to deliver vast improvements to Britain's rail infrastructure with a £37.9bn budget for 2014-19.

Sir David had been after £40.1bn, but the Office of Rail Regulation trimmed more than £2.2bn from Network Rail's business plan in what it described as a "stretching, but achievable" budget.

Mr Kirby's £63,708 bonus was also scrutinised by the organisation's critics, but his credentials have been buoyed by the successful launch of Network Rail Consulting, which he chairs. This is a commercial operation designed to make money through advisory work overseas and recently won a role working with Amtrak on upgrading the US's busiest rail line between Boston and Washington DC via New York.

Mr Kirby has strong support among several of the body's non-executive directors, but chairman Richard Parry-Jones is believed to have identified a strong candidate from the car industry. Such a background would clearly appeal to Mr Parry-Jones, as he started his career with Ford and was awarded a CBE for services to the motoring industry.

Sir David is to step down next April, having only been in the job since 2011. However, it is understood the recruitment process is moving apace, which could hasten his departure.

The next chief executive will also have to tackle Network Rail's growing debt mountain, which has soared past £30bn. The organisation spends £14m a day on tracks, signalling and expanding Britain's railways.