The main index added 0.3pc, as Asia-focussed HSBC and miners gained on the prospect of an initial U.S.-China trade deal. A softer pound also helped blue-chip exporters such as Reckitt rise.
The FTSE 250 edged 0.1pc lower, as publisher Future Plc weighed with an 11pc slide following a discounted share placement. Its shares were on track for their worst day since mid-June.
The mid-caps, however, still hovered around a near 15-month high scaled earlier this week.
The index has climbed 3.5pc higher since Oct. 29, when parliament approved Prime Minister Boris Johnson's call for a general election.
Markets see a prospective victory for Johnson's Conservative Party as the most likely scenario for Brexit to be delivered by the Jan. 31 deadline. As such, the pound weakened slightly after polls showed the Conservative lead was narrowing.
The broader mood was firmly upbeat after Trump's comments on trade following a telephone conversation between senior U.S. and Chinese negotiators, though CMC Markets analyst Michael Hewson hollered caution as the Dec. 15 deadline for new tariffs draws closer.
"It still remains unclear what the timing is likely to be on the agreement of a phase one deal," Hewson said. "However with three weeks until Dec. 15, it's not hard to imagine that it is highly unlikely that we'll get anything tangible before that."
Washington's support of pro-democracy protesters in Hong Kong may also be a sticking point in negotiations.
News-driven moves were scant, though soft drink company Britvic, which owns the Tango, J2O and Fruit Shoot brands, slipped 3pc after its annual profit slumped nearly a third.
"The guidance statement is light on the detail but we suspect consensus FY2020 to come down a few percentage points," Liberum analysts said.