The FTSE index was up 0.4 percent and the midcaps were 0.7 percent higher by 0950 GMT.

Housebuilders Persimmon, Barratt and Taylor Wimpey - among those most vulnerable to a no-deal Brexit - were among the biggest gainers after midcap Galliford Try reported higher first-half profit that topped Liberum estimates.

Galliford led the FTSE 250 with a 5.3 percent gain, hitting its highest since end-November.

A trader also cited growing hopes that Brexit could be delayed if a EU divorce deal agreeable by all parties is not reached by March 29.

Britain's exit from the bloc remains unclear with just over six weeks until the deadline as Prime Minister Theresa May on Tuesday asked lawmakers to give her more time to negotiate a deal acceptable to both Brussels and parliament.

Britain's economy will barely grow in the run-up to Brexit amid concerns of a no-deal, but if there is agreement there will be a modest post-divorce upturn, according to economists polled by Reuters.

Inflation in Britain fell to a two-year low in January, dipping below the central bank's target and offering some respite to households ahead of Brexit.

Elsewhere, Asian stocks touched a more than four-month high on optimism that the United States and China might be able to hammer out a deal to resolve their protracted trade dispute.

That lifted shares of Asia-focussed companies, with HSBC and luxury brand Burberry rising 1.1 percent and 1.7 percent, respectively.

"With the ongoing negotiations in Beijing paving the way for Thursday's top tier tete-a-tete ... the pressure may have been taken off oh so slightly following some interesting comments from Donald Trump overnight," Spreadex analyst Connor Campbel said.

Global miners were on course for their best day so far this month as London copper prices were headed for their first session of gain in five.

The best FTSE 100 performer was packaging group DS Smith which rose 4 percent as rival Smurfit Kappa said the current year had started positively after reporting strong results. London-listed shares of Smurfit Kappa also added 2.5 percent.

Rolls-Royce followed with a 2.5 percent gain. It rose to a four-month high after a rating upgrade from Credit Suisse.

Tour operator TUI underperformed with a 3.7 percent fall, extending losses from the previous session when it posted a bigger first-quarter loss.

In a similar vein, online trading platform Plus500 declined 4.4 percent after losing nearly one-third in value on Tuesday when it issued a profit warning.

Supporting the midcaps was Dunelm that rose 4 percent after reporting a jump in first-half earnings.