A question mark has been placed over proposals to redevelop the former RAF Coltishall base, after heritage watchdogs objected to proposals to dig up part of the runway.

Norfolk County Council bought the base for £4m in January last year and hopes to recoup some of its investment by removing the ends of the runway and using an estimated 140,000 tonnes of aggregates for road improvement schemes, such as the £19m Postwick Hub junction near Norwich.

The decision on whether to grant planning permission for the ends of the runway to be dug up rests with the council, but English Heritage has written to the authority urging it to turn down the application, which has been submitted by council contractor Lafarge Tarmac.

The letter says: 'English Heritage considers that the removal of these runway extenstions would neither preserve, nor enhance, the character or appearance of the conservation area, but would result in harm to this, and the designated blast walls within the base.'

English Heritage say, on the basis of the information submitted, the application should be refused, because it would 'result in harm to two designated heritage assets, namely the RAF Coltishall Conservation Area and the Scheduled eastern grouping of Cold War era blast walls'.

The letter adds that, although the southern grouping of Cold War era blast walls are not a designated heritage asset, they are 'demonstrably the equivalent of a Scheduled Monument'.

They argue that removing parts of the runway would 'change our understanding of the designated blast walls and therefore would result in harm to their significance.'

The letter says national planning policies require 'great weight' to be given to conserving designated heritage assets and that harm must be 'weighed against any wider public benefits'.

It continues: 'Given the degree of harm that would result from this proposal, English Heritage would expect that a high level of public benefit would be required to outweigh that harm', before adding it is 'unclear' from the application what is proposed to address that.

A spokesman for Norfolk County Council said: 'A report is being drawn up for members to consider next month and we continue to encourage people to respond to the planning application. Members of the public have up to March 20 to give their views.'

The application will be considered by the county's planning sub committee on Friday, March 21, while Scottow Parish Council will hold a meeting at St Edward's Church in Badersfield tonight to discuss the future of the site.