The campaign to force a U-turn on plans to charge 20% VAT on alterations to listed buildings was ratcheted up a notch this week.

The Heritage Alliance, a coalition of 90 bodies including the Architectural Heritage Fund and the RIBA Conservation Group, has written to every MP setting out the “devastating implications” of the tax hike and urging them to speak up in the Commons.

And a petition against the change has been signed by around 14,000 people, making it the highest “trending” e-petition on the Downing Street website.

Campaigners have just two weeks to convince George Osborne to reverse the announcement, made in last month’s Budget, to scrap the zero rating for alterations.

Repairs to listed buildings already attract the full 20% VAT.

Last week bishops and other church leaders predicted the move would cost the Church of England ￡20 million a year. Some 45% of grade I listed buildings are churches.

And architects warned it was not just churches and cathedrals that would be hit but a whole range of historic buildings including warehouses, museums, follies and private houses — and not just stately homes.

“The chancellor says it’s a rich man’s tax but it’s blatantly not,” said Peter Drummond, chairman of the Architectural Heritage Society of Scotland.

“Around half the listed buildings in Scotland are houses — people’s homes, ranging from Victorian cottages to Edwardian terraces; and the situation is broadly similar in the rest of the UK.

“This comes at a time when grant funding is under great pressure. There’s simply not the capacity in the system for costs to increase by up to 20%. 

“A lot of heritage-led regeneration will fail at the feasibility stage which will mean a lot less work for everybody in our profession,” he said. He predicted it would take two or three years for the full impact to be felt because of the longer lead times necessitated by fundraising.

And Nick Berry, associate director at OMI Architects, said that two church projects OMI was working on could both now be hit by delays.

“Adding to budgets affects projects’ viability,” he said. “It will potentially have quite a drastic effect, especially for practices working predominantly in heritage.”