Jeremy Westlake, the CFO of Network Rail, took a flight from Birmingham to Glasgow which saved roughly £60 on train fares

The bosses of the UK's largest railway operator are being told to take flights for work trips because they are cheaper than the train.

Network Rail's expenses policy orders company staff to use air travel when it is the less expensive option and it has been revealed that employees took 9,212 national flights over the past two years.

Train fares have swelled in recent years, jumping by 3.4 per cent in 2018 and 3.1 per cent this year.

Of the thousands of flights taken by Network Rail staff, 17 were by high-ranking executives including chief financial officer Jeremy Westlake.

In July 2017, Mr Westlake flew from Birmingham to Glasgow for £47.99, according to data obtained through a freedom of information request made by the Sunday Times.

Current train fares between the West Midlands and Scottish cities cost roughly £115, making the pre-hike July 2017 rough price £108 - £60 more expensive than the flight.

The company's policy states: 'Network Rail's expenses policy states: 'UK air travel should be used where it represents the most cost effective option compared to the relevant train fare, when taking into account the total cost of the journey.'

Train fares have swelled in recent years, jumping by 3.4 per cent in 2018 and 3.1 per cent this year

Network Rail's expenses policy orders company staff to use air travel when it is the less expensive option

But the operator, which spent £1million on staff rail fares over the past two years, insists that the bulk if its travel expenses are made up of train rides.

A spokesperson said: 'With 98% of our business travel made by rail, trains more often than not represent best value.'

However, huge price gaps often exist between plane and rail travel.

The cheapest logged plane journey of a Network Rail employee was a £19.99 flight from Cardiff to Anglesey - saving £60 on the typical £84 train fare.