Hundreds of game birds escaped from a country estate used by Sheffield MP and Deputy Prime Minister Nick Clegg.
Animal rights activists are suspected of targeted the Chevening Estate, Kent, freeing birds being reared for game shooting.
About 380 birds are thought to have flown away, leaving just 20 behind.
The estate is used as a weekend residence by Mr Clegg, Liberal Democrat MP for Sheffield Hallam, and Rotherham-born Foreign Secretary William Hague.
A Kent Police spokesman said: “The roof of some game pens on property off Chevening Road were damaged allowing birds to escape.
“We are not ruling out the possibility of it having been carried out by animal rights activists.”
The incident happened at the estate last week.
The estate refused to comment on the birds’ release, saying the shoot and associated enclosures were sub-let to a tenant.
The Government-owned Chevening House and estate consists of 3,000 acres, including a lake and maze in the grounds, and 530 acres of mixed woodland.
The grace-and-favour property was built in the 17th Century and has 115 rooms.