A leading firm of architects and planning consultants is at the centre of a row over a conservatory in the garden of a 16th century house overlooking the River Thames in Abingdon.

David Tetlow, left, and Michael Black, who both oppose the conservatory pictured behind them

Neighbours said it is an "eyesore and a monstrosity" and should be removed. The owners reject the criticism and said the conservatory would stay.

West Waddy ADP moved from Bury Street into its new headquarters in the Malthouse at the bottom of East St Helen Street. The company renovated the buildings and incorporated two houses on the site, one with a conservatory.

One of 40 signatories on a petition to the Vale of White Horse District Council is that of the chairman of the East St Helen Street Residents' Association David Hardy.

He said: "The conservatory is an eyesore and a monstrosity. It is completely out of scale and character in this environment and ruins the finest riverside townscape upstream of Henley. Oxford has nothing to match."

He said everyone was astonished that the architects could conceive and Vale of White Horse District Council planners condone the conservatory. Opponents are urging the council to re-think the original decision, withdraw permission and order the removal of the conservatory.

But council planners stand by their decision. Area planning officer Mike Gilbert said: "This was a listed building application. We were well aware of the sensitivity and it was approved on its merits.

"We received no objections from the town council or local residents."

Mr Gilbert said the timber framed and brick conservatory was on the site of what was once a much bigger structure. He added: "I think what is upsetting some people is that the conservatory is much more noticeable than the old and somewhat tatty building that was there before."

Philip Waddy of West Waddy architects said he was surprised by the opposition. He said: "We have gone through the proper channels and have received listed building consent from the council planners. We have done everything right and are pleased with the whole renovation scheme. I'm sorry some people don't like it, but the conservatory is staying."