Work to replace most of the 20th-century floor joists in the living room at Lacock Abbey has been blasted as “falsifying history”.

The National Trust had applied for retrospective planning permission to replace the rotten timber floorboards at the west flat in the Grade I listed building.

A spokesman for the National Trust said: “This was a small repair job to a 20th-century floor with rotten timbers – work which wouldn’t normally need consent.

“However, the more we opened up the floor, the more we found was rotten and needed replacing. We spoke to the local council planners and were asked to submit retrospective application – which has now been approved.”

In their report, Wiltshire Council’s planning officer said the boards were replaced with new or reclaimed softwood from other National Trust properties in Lacock.

They said: “The methodology of replacement rather than other forms of repair such as doubling up has resulted in the loss of more historic fabric than necessary.”

The officer added that the use of the reclaimed wood “falsifies the history of the floor” and questioned why the replacements were not originally done using timber oak.

The report continued: “Had these proposals been submitted prior to works being carried out they would not have been supported in this form.

“Unfortunately, the work has already been carried out, the early 20th century timber lost and timber from nearby buildings used for some of the work.

“In this particular case, the work will be accepted and consent for its retention granted.”

The officer’s report warned that this should not happen with future repair or restoration works submitted for Lacock Abbey.

The National Trust spokesman added: “We always listen to advice from local council conservation officers when seeking planning consent.”