Where is the prime minister office UK?

He works from home at 10 Downing Street and at the House of Commons which is about 300 yards away.
The Prime Minister has his own office in the Palace of Westminster, and also has an office suite at his official home in no.10 Downing Street. These two places are where he does most of his work- processing documents, reading letters from the public, holding Cabinet meetings with his Government ministers, assessing petitions, meeting VIPs and so on.

But he also has a country residence called Chequers, which has been the country retreat of the British Prime Minister since it was gifted to the office of PM by the nation in 1917. Here he can also receive important guests and entertain them, use it as a retreat at which to ponder over serious issues and how they might be resolved, or simply for a break in which to 'get away from it all' for a while.