(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 0.1%, FTSE 250 off 0.2% Dec 11 (Reuters) - London’s mid-cap index slipped on Friday on fears of a tumultuous no-deal Brexit in three weeks, while GlaxoSmithKline dipped after announcing a delay in its efforts to develop a COVID-19 vaccine. The drugmaker dropped 0.2% after it said the experimental vaccine it was developing with France’s Sanofi showed an insufficient immune response in clinical trials and it now hoped to come up with a more effective vaccine by 2021 end. Sanofi’s Paris-listed shares were down 2%. The domestically-focussed FTSE 250 slipped 0.2%, deepening losses of more than 2% this week, as Prime Minister Boris Johnson said there was “a strong possibility” Britain and the European Union would fail to strike a new trade deal. The blue-chip FTSE 100 shed 0.1%, with declines in consumer staples and mining stocks more than offsetting a jump in financial stocks. Banks, the worst-performing FTSE sector this week, rose 0.7% as the Bank of England said they could resume paying some dividends and bonuses. (Reporting by Sagarika Jaisinghani in Bengaluru; Editing by Arun Koyyur)