(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window) * FTSE 100 up 0.4%, FTSE 250 adds 0.3% Dec 17 (Reuters) - London’s mid-cap index rose on Thursday as investors awaited a post-Brexit trade deal to avoid a messy exit for the UK from the European Union, while higher oil prices helped lift the commodity-heavy FTSE 100. The domestically focussed FTSE 250 index, considered a barometer for Brexit sentiment, rose 0.3% and looked set to gain for a fourth straight session. The blue-chip FTSE 100 added 0.4% as oil prices hit a nine-month high after a fall in U.S. inventory and on optimism over a U.S. stimulus package. Oil majors BP and Royal Dutch Shell were among the biggest boosts to the index. The European Union’s chief executive said Brexit talks have moved closer to sealing a new trade deal but it was still unclear if they would succeed with just over two weeks left for Britain’s transition period out of the bloc to expire. All eyes will be on a Bank of England meeting later in the day where the central bank is expected to keep its policy unchanged. WPP, the world’s biggest advertising company, jumped 2.7% after saying it expected to return to its 2019 level of net sales by 2022. (Reporting by Shivani Kumaresan in Bengaluru; editing by Uttaresh.V)