Runnymede Borough Council has ordered Conservative party donor Surinder Arora to demolish all or part of the Fairmont Windsor Park Hotel.
The five-star hotel played host to the signing of the Windsor framework in February, when the UK and the EU agreed on post-Brexit trading agreements for Northern Ireland.
Last month, the Surrey council issued an enforcement notice after the hotel was extended without permission in breach of planning regulations.
The notice ordered that the breach be remedied, by making the hotel comply with its planning permission, or that the building be demolished in its entirety.
Mr Arora, CEO of the Arora Group, has until October to appeal.
He said: ‘We are truly sorry for the mistakes made during the construction of the Fairmont Windsor Park. It was a highly challenging construction site being developed in the middle of the Covid-19 pandemic.
‘We are now constructively engaging with Runnymede Council and other local stakeholders to find mutually acceptable solutions to the planning concerns which have been raised.
‘The hotel is a fantastic property which we want to ensure it continues serving the local area and bringing significant economic benefits to Runnymede. We remain extremely proud of it but also accept the need to remedy our mistakes.’
