Conservationists are battling against a leading British architect to save what they believe to be one of the capital's finest Art Deco buildings.

The headquarters of SmithKline Beecham, which stands on the Great West Road in Brentford, west London, was built as an aircraft components factory in 1937.

It is described by heritage watchdogs as 'among the most significant surviving buildings associated with the Second World War'.

But the pharmaceutical company is proposing to sweep away the Grade II listed building to replace it with a development designed by Richard Rogers, one of Britain's foremost architects.

The Lloyds building in the City of London and the Pompidou Centre in Paris are among his best known works.

Designs for the 14 acre Great West Road site are being drawn up for a joint venture between SmithKline Beecham and British Land, a property development company.

The one million sq ft development will provide office space for multi-national companies.

Julian Holder of the 20th Century Society, a charity set up to protect buildings built after 1914, said that in addition to being a historic building, the Beechams factory is a key component in a historic stretch along the Great West Road which boasts a profusion of fine Art Deco buildings.

Many conservationists are deeply concerned about the threat to historic buildings posed by new developments since Lord Palumbo was given permission to demolish the eight listed Victorian buildings on the No 1 Poultry site in the City of London.

It is to be replaced by a post-modernist building designed by the late Sir James Stirling.

Hounslow council's planning committee will meet in the next few months to consider whether to give the Richard Rogers scheme outline planning permission.

Simon Smithson, of Richard Rogers Partnership, said the retention of the Beecham's factory 'would make it impossible to realise the full potential of the site'.

He said that since the building of the M4 flyover nearby, it was impossible to view the front elevation as it was meant to be seen. The building was no longer set in its original context, he said.

The proposed new development continues 'in the spirit of the Great West Road' and is 'more in tune' with the current scale of the surrounding area.

The Beechams Factory, as the building is known, was originally built for Simmonds Aerocessories during an era when the budding British aircraft industry based itself largely in north and west London - though few traces of this still remain. The architects were Wallis, Gilbert and Partners.

Aeronautical motifs still remain, such as the figure of a pilot with an eagle perched on his shoulder, which stands on top of the central tower. Two years after the end of World War II, it was bought by BOAC who converted it into offices. It was sold on to Beechams in 1955.

Recent research by the Royal Instuition of Chartered Surveyors and English Heritage suggested that listed office buildings perform as well or better than their competition as investments.

A survey of 2,500 office building across Britain showed the average return on a listed building was 8.5 per cent per annum. That compared with a figure of 7.3 per cent for unlisted modern building and 7.8 per cent for unlisted pre-war buildings.