The blue-chip index climbed 0.9% to a near one-month high, taking home gains for the fourth consecutive session and outshining the European benchmark.
A sell-off in the pound ahead of the European Union's decision on whether to grant Britain another Brexit extension and amid risks of a possible general election led the domestically focussed FTSE 250 <.FTMC> 0.1% lower.
The past two weeks have taken UK shares from pillar to post with major Brexit developments including Prime Minister Boris Johnson striking a new Brexit deal with the bloc and lawmakers at home forcing his hand into asking for another extension to the divorce.
Reflecting the anxiety ahead of EU's decision on the way forward, a sub-index of homebuilders <.FTNMX3720> - a sector considered among most vulnerable to the British economy - dipped 1% on its fourth straight session in the red.
UK blue-chips, on the other hand, accelerated early gains as a weakening in the local currency boosted dollar earners in the index including GlaxoSmithKline Plc and HSBC Holdings Plc.
The bourse was already cheery after a survey showed French business activity picked up more than expected in October.
'U.S.-CHINA AND BREXIT IN LIMBO'
The FTSE 100, whose components rake in more than two-thirds of their earnings in U.S. dollars, is on course for its best weekly performance since early February, as uncertainties over the course of UK's EU departure have dented the value of sterling.
AstraZeneca Plc contributed to nearly one-third of the gains for FTSE 100 after the pharmaceutical firm raised its annual product sales forecast for the second time this year. The stock jumped nearly 6% on its best day in three months.
Analytics and decision tools provider Relx Plc and industrial software company Aveva Group Plc added 4% and 5%, respectively, following trading updates.
"There's not been a huge catalyst for markets this week. Earnings are largely topping beaten-down estimates. U.S.-China and Brexit are in limbo," Markets.com analyst Neil Wilson said.
On the other end of the spectrum was Royal Bank of Scotland Group Plc that skidded 3.3% as it swung to a third-quarter loss due to a fresh 900 million pound provision to settle mis-selling claims.
Woodford Patient Capital Trust Plc, formerly run by once-star money manager Neil Woodford, surged 25% as the company appointed asset manager Schroders Plc as its new portfolio manager.
Metro Bank Plc jumped 11.5%, despite a grim third-quarter earnings report, with a trader saying retail investors saw a buying opportunity after the troubled lender's CEO hinted that the company could consider takeover offers.
(Reporting by Muvija M and Shashwat Awasthi in Bengaluru; Editing by Shounak Dasgupta and Lisa Shumaker)
By Muvija M and Shashwat Awasthi