Uncertainty remains over the full delivery of a Norwich in 90 rail service as further investment has to be secured by Network Rail despite the most ambitious programme of upgrades in the region announced by Abellio today.

Beginning in October 2016, the new Greater Anglia franchise will run until 2025 and involve billions of pounds of investment as the Dutch Railways-owned company is spending £1.4bn on new trains and paying the Treasury £3.7bn.

Over the term of the franchise the entire fleet of trains will be replaced and upgraded to include WiFi, and journey times across the network will be reduced.

But with only two services a day scheduled to achieve travel between Norwich and London in an hour and a half, Abellio Greater Anglia managing director Jamie Burles said any further progress depends on infrastructure upgrades. 'We will take the full benefit of the new rolling stock such as better acceleration and less dwell times in stations and fundamentally restructure the timetable in 2019 to allow the speeding up of services,' he said.

'We have pushed all these things to the maximum, and for further improvement we would need infrastructure enhancement. We wanted to guarantee what could be achieved through the timetable and rolling stock – the things we are 100pc in control of.'

A spokesperson for Network Rail said over the next three years overhead lines in the region will be renewed.

'We need to work to secure the investment to continue delivering improvements for passengers from 2019 and beyond,' they added.

Mr Burles said he is 'convinced' of Network Rail's ambition to continue to enhance infrastructure but he is unable to make guarantees. 'We did not want to overpromise what could be delivered by Network Rail,' he said. 'We are in conversation about what could be done such as reducing the number of level crossings and temporary speed restrictions.

'There is a plan in place with Network Rail to look at what further, if anything, could be done in terms of infrastructure enhancement to allow us to go even better.

'We are in direct control of 30pc of the delays on the network and that means we are not in control of 70pc of the delays which occur. Customers need to see that transformation across the board – the delays we are responsible for and those externally. We have to, along with Network Rail, ensure this happens. The replacement of overhead lines is a key element of that.'

Mr Burles added 'there is no Plan B' for upgrades in the region, and no clause in the contract for compensation if external factors mean they are unable to deliver.

'There is no recompense for us and this is why in terms of incentives we have to achieve Plan A. We need the improvement and reliability which turns into the revenue which allows us to pay the amount of money we committed to paying to the government.

'Irrespective of where the delays come from we need to reduce them enough to hit our targets. If I thought we could not achieve that target I would not have agreed to run the business moving forward.'