London's blue-chip bourse was up 0.7 percent at 0850 GMT after hitting its highest since Dec. 6 and the mid-cap index was up 0.8 percent at its loftiest since Dec. 5.
European and Asian markets rallied after talks in Beijing with Washington over trade concluded earlier on Wednesday as the world's two largest economies tried to seek a truce to end a longstanding row.
A U.S. trade delegation member said "it's been a good one for us" and the Chinese foreign ministry said results of the negotiations will be released later.
At home though, uncertainty over the UK's divorce from the European Union deepened ahead of next week's vote on the draft deal in Parliament.
British Prime Minister Theresa May's government cautioned lawmakers on Wednesday that it was a delusion to think that the government would be able to negotiate a new divorce deal with the European Union if parliament voted down her deal due on Tuesday.
Her government suffered a defeat in parliament on Tuesday night when lawmakers who oppose leaving without a deal won a vote on creating a new obstacle to a no-deal Brexit.
Still, housebuilders, one of the most battered sectors amid concerns about the slowing economy due to Bexit - led the gains on Wednesday after Taylor Wimpey maintained its 2018 results forecast and forecast solid 2019 sales.
The shares were up 4.1 percent, topping the blue-chip leader board and on track for their best day since July 2016, taking peers Persimmon and Barratt with them.
Sainsbury's shares slipped almost 3 percent in early deals on a worse-than-expected fall in underlying sales in the key Christmas quarter. By 0856 GMT, they were down 0.75 percent in choppy trading.
The update comes just a day after peer Morrisons also missed sales forecast for the key period, while Tesco bucked the trend and led a rally after industry data covering the Christmas quarter sales.
Among mid-caps, IT infrastructure and service provider Softcat surged over 14 percent after a positive trading update, while fashion retailer Ted Baker followed with a 6.4 percent rise on higher retail sales in the holiday period.
Baker Greggs also rose 5.1 percent after it flagged a "very strong" finish to the year.