The FTSE 100 was up 0.1% by 0720 GMT while the FTSE 250 was down 0.5%.
Interest in stocks considered safe bets during uncertain times was high as trade negotiations between Washington and Beijing seemed to be at a deadlock.
Oil majors Shell and BP gained as oil prices rose on concerns about supply disruptions in the Middle East.
British Gas owner Centrica added 2% after it maintained its annual operating cash flow and net debt forecast despite a challenging trading environment.
Metro Bank, which has lost more than two-thirds of its value this year, slipped 7.8% to hit another all-time low on the mid-cap index.
It said on Friday its plan to raise equity was well advanced, while a Financial Times report on Sunday said the bank was looking to sell loans that were hit by an accounting error.