China reported its lowest number of new coronavirus cases since late January, bolstering a forecast by Beijing's senior medical adviser for the outbreak in the country to end by April even though fears of further international spread remained.
That helped the FTSE 100 add 0.50%, with an additional boost to the blue-chip index from oil majors Shell and BP, as they tracked a surge in crude prices.
Miner Anglo American rose 4.9% as UBS raised its rating on the stock.
The FTSE 250 added 0.68%, led by payments company Finablr. Home furnishings retailer Dunelm which jumped 8.7% after an upbeat profit forecast.
Online trading platform Plus500 also supported the mid-cap index with a 4.6% rise as its second-half core earnings nearly doubled from the first.
Slightly more than 2,000 new confirmed cases took China's coronavirus total to 44,653. That was the lowest daily rise since Jan. 30 and soothed public fears and markets on hopes of an end to disruption in the world's second-largest economy.
"While there continues to be high uncertainty about the rate of spread and timing of the peak of the coronavirus, modelling by epidemiological experts indicates a likely range for the peak between late February and June," analysts at S&P Global said.
CMC Markets analyst David Madden said the impression is the Chinese government are more in control of the crisis, and that has boosted sentiment, with the FTSE at its highest level since late January.
Dealers also took note of comments overnight from U.S. Federal Reserve Chair Jerome Powell, who remained fairly upbeat about the U.S. economy, but warned that the virus-led disruptions in China could spill over globally.
"One can, in fact, make a bullish case for equities based on any scenario regarding COVID-19," OANDA analyst Jeffrey Halley said.
"An escalation in its spread causes a pronounced global slowdown, which prompts central banks to cut interest rates aggressively. Buy equities for the V-shaped recovery."
Britain's benchmark stock indexes have mirrored volatile swings in global markets over the past few weeks as the coronavirus spread.
Among stocks, bullish brokerage actions lifted shares in corporate services firm Sanne Group by 10% on the FTSE 250.
Arbuthnot Banking soared 11.6%, after guiding to annual profit at the upper end of market expectations.
By Shashwat Awasthi and Noor Zainab Hussain