(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window) * FTSE 100 falls 0.3%, FTSE 250 flat Dec 15 (Reuters) - The FTSE 100 slipped on Tuesday as tougher restrictions were imposed in London to curb a resurgent COVID-19 pandemic, while investors awaited a Brexit trade deal with the European Union before a year-end deadline. The blue-chip FTSE 100 index was down 0.3% by 0803 GMT, with healthcare and financial stocks leading the declines. The mid-cap FTSE 250 index, considered a barometer for Brexit sentiment, was flat. London will move into England’s highest tier of COVID-19 restrictions on Wednesday, with additional curbs on restaurants and socialising, due to increased infection rates that may be partly linked to a new variant of the coronavirus. In company news, online trading platform IG Group Holdings Plc gained 1.6% after forecasting a surge in first-half revenue as coronavirus-led volatility in financial markets stoked strong client activity. (Reporting by Shivani Kumaresan in Bengaluru; editing by Uttaresh.V)