Campaigners attempting to speed up the main rail line between London and East Anglia have written to Transport Secretary Patrick McLoughlin asking for renewed assurances that upgrades will be delivered on time.

The Great Eastern Main Line Taskforce has also written to new Network Rail chairman Sir Peter Hendy asking for the same assurance.

The campaign is backed by more than 100 of the region’s most senior business and education leaders and the Chancellor reaffirmed his commitment for ‘Norwich in 90’ and ‘Ipswich in 60’ in his Summer Budget.

But to ensure continued momentum the letters stress that improvements to the main line are vital to the region’s economy and seek assurance that the Department for Transport and Network Rail will deliver their share of improvements as promised.

The letters say: “The improvements that our report outlined are crucial to the Eastern regional economy and we trust that they will still be delivered as promised.”

They were sent after the Transport Secretary gave an update about Network Rail’s performance and announced the government would “pause” a number of planned improvements across the country.

In his statement, Mr McLoughlin repeated his commitment to bring about “modern, faster trains to Ipswich and Norwich in the next franchise.”

Mark Pendlington, chairman of New Anglia LEP, said: “Our hard-fought campaign is backed by businesses and long-suffering rail passengers across the three counties and improvements to track and train are vital to East Anglia and UKplc.

“We have commitment from Government for the investment we need and our job now is to keep up the pressure, make sure words turn into action and that we all see year-on-year transformation of the Great Eastern Main Line towards Norwich in 90, Ipswich in 60 and Colchester in 40.”

Last month, the Department for Transport announced the three train companies shortlisted to bid for the new franchise.

These companies will now submit their bids to government by August 2015 showing how they will achieve the recommendations of the Great Eastern Rail Report – including all new rolling stock.

The new franchise will start in October 2016.

However the speed improvements can only be achieved if there are also major track upgrades – like the construction of a third line between Chelmsford and Witham in Essex and a complete rebuild of Haughley Junction near Stowmarket.

Network Rail also wants to close a number of level crossings on the main line.