The application includes making the pub’s basement, which is home to Storey’s Wine Bar, in to residential flats and would mean the pub is behind scaffolding for up to two years.
Concerns have also been raised about the impact flats would have on the surrounding area, which is well- known for having crowds drinking outside and opposite the pub.
The Publican's Morning Advertiser is awaiting a statement from the pub's current owners, brewer Shepherd Neame.
Joining supporters outside the Westminster Arms earlier this afternoon, Nigel Farage said: “We’ll do what we can to help save the Westminster Arms. The plan to build apartments here is more corporatism destroying our culture. I’ll be putting my objection to the development plans into Westminster Council this afternoon.”
A website started this morning called save the Westminster Arms has attracted thousands of views and hundreds have already submitted their objection to the council.
Campaigner and local Raheem Kassam told the PMA that it would difficult for the pub to survive without the wine bar, which is a strong source of revenue.
He added that the next step in the journey to save the pub will be approaching its influential neighbours, which include the Conservative party headquarters, the Treasury and the Spectator magazine for support.
CAMRA greater London pub protection adviser James Watson warned other pubs in London may face similar challenges thanks to sky high property prices.
“Pubs across the capital are being threatened with closure as property values continue to rise and developers look to exploit weaknesses in the current planning system for their profit. We would urge Westminster council to do everything in their power to ensure this valued community pub remains open for the public, MPs and government ministers to enjoy a pint of real ale in - as they have done for many years."