The FTSE 100 fell 0.5% as the oil and gas sector <.FTNMX0530> declined 1.8%.
Royal Dutch Shell hit its lowest in more than six-months after warning third quarter production was set to drop sharply due to the coronavirus pandemic and hurricanes forcing offshore platforms to shut down.
Compass Group lost 3.2% as the catering giant forecast a 19% fall in organic sales and a 100 million pound ($128 million) hit on its biggest businesses.
Sentiment took a hit after an indecisive U.S. presidential debate overnight and a near 20% slide in Britain's GDP, but investors took heart from upbeat economic data from China and the United States.
Brexit uncertainty coupled with fears of further economic stress as COVID-19 cases rise again washed out the FTSE 100's August gains. On the quarter it lost almost 5%.
"The fourth quarter is going to really be interesting: we'll hopefully get some news that takes away some of the unknowns such as a new U.S. President and indications on when we can get a coronavirus vaccine," said Jonathan Bell, chief investment officer at Stanhope Capital.
"Valuations are quite high, but I'm optimistic that quality growth stocks will continue to outperform. That's the right place to be in the fourth quarter."
The mid caps index rose 0.8% as 888 Holdings jumped 21% after forecasting a better annual profit and declaring a special dividend.
G4S was the top boost, hitting a seven month high after the security group rejected a cash offer by smaller Canadian rival GardaWorld that valued the British company at 2.97 billion pounds ($3.81 billion), weeks after it turned down a similar proposal.
By Shashank Nayar and Susan Mathew