UPDATE 1-London stocks begin 2021 with gains; Ladbrokes owner soars

* UK’s FTSE 100 jumps most in nearly two months

* Ladbrokes owner Entain surges on merger proposal

* Plumbing parts maker Ferguson sells UK business

* FTSE 100 up 2.5%, FTSE 250 adds 1.4% (For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window)

Jan 4 (Reuters) - British shares jumped on Monday in the first trading session of the new year as optimism around vaccine rollouts kept the sentiment afloat, while a jump in metal and energy prices helped boost the export-heavy FTSE 100 index.

The blue-chip index rose 2.5% on its first day of trading with Britain outside the European Union’s orbit, with shares of Entain being the top gainer.

The Ladbrokes owner surged 24.5% after saying it received proposals from U.S. casino operator MGM Resorts for a possible offer.

“Traders have an idea that the COVID-19 situation is coming back under control with vaccine rollouts in place and the fact that Britain could exit the European Union with a deal in hand continues to support sentiment,” said David Madden, an analyst at CMC Markets.

Mining shares and oil majors were among the top gainers, with Rio Tinto being the biggest boost on the index. BP and Royal Dutch Shell advanced between 3% and 3.5%.

The mid-cap index jumped 1.4%.

However, limiting gains was Prime Minister Boris Johnson’s announcement on Sunday that tougher lockdown restrictions were probably on the way as COVID-19 cases keep rising.

Analysts at Deutsche Bank say markets would now be closely watching any issues with COVID-19 or the vaccine rollout, given that the new coronavirus variants, found in the UK and South Africa, have been detected in several other countries.

Plumbing parts distributor Ferguson Plc reversed early gains to drop 0.2% after it agreed to sell its UK-focused business to private investment firm Clayton, Dubilier & Rice for about 308 million pounds ($421.56 million).

Drugmaker AstraZeneca jumped 2.0% after Britain was set to roll out its low-cost and easily transportable COVID-19 vaccine, the second vaccine candidate to be distributed. (Reporting by Shashank Nayar in Bengaluru; editing by Uttaresh.V)