Prime Minister Theresa May's announcement that she will trigger Article 50 by the end of March next year sent the pound tumbling to a three-month low against the dollar to $1.28.
The pound was also at a three-year low against the Euro at €1.14.
Chancellor Phillip Hammond unveiled a £5 billion housebuilding stimulus package at the Conservative Party conference, pushing Travis Perkins 3.1% higher to £15.91, with Barratt Development (BDEV) and Taylor Wimpey (TW.) also in positive territory.
The FTSE 100 jumped 1.2% to 6,984, boosted by the impact of the weaker pound on overseas earners and by both Royal Dutch Shell stocks (RDSA and RDSB), which jumped more than 2%.
West Texas Intermediate (WTI) crude oil was flat at $48.23 and Brent crude oil rose 0.2% to $50.28 per barrel, respectively.
Gold nudged lower to $1,310 per ounce and copper slumped 0.9% to $4,806 per tonne.
The FTSE 250 advanced 1.7% after the UK Purchasing Managers' Index (PMI) reported its highest levels in September since 2014, as a result of growth in output, new orders and employment.
The PMI index was 55.4, which was ahead of expectations and the 53.3 posted in August.
MID CAP RISERS AND FALLERS
Fund manager Henderson Global Investors (HGG) climbed 16.7% to 270.8p on news of a merger with US financial group Janus Capital, which will result in the combined group trading on the New York and Australian stock exchanges.
Aberdeen Asset Management (ADN) gained 4.9% and Jupiter Fund Management (JUP) rose 6% following the news as M&A chatter lifted the investment industry.
Global medical products group ConvaTec said it will float on the London stock market in late October or early November. It said it wants to raise $1.8 billion to help pay down debt.
Jefferies International recommended 'buy' for Virgin Media (VM.) with a price target of 400p, causing the broadband provider to trade 4.5% higher at 325.1p.
SMALL CAP RISERS AND FALLERS
Investors were pleased with Tethys Petroleum's (TPL) announcement that the Almaty City Court's Board of Appeals found in favour of Tethys by dismissing the appeal of the claimant and upholding an earlier decision in August to lift the seizure order over the company's assets.
St Peter Port Capital (SPPC) commenced a review of strategic option for the company, which may include a potential sale of the firm. Shares in the company traded 22.4% to 15p.
Full scale zinc production started at Vast Resources' (VAST) Manaila polymetallic mine in Romania, providing the company with a second revenue stream, which triggering a share price rise of 9.1% to 0.3p.
Financial administration group Sanne (SNN) rose 4.2% to 476p on news it will buy American rival FAS for $52.6m, giving it a base from which to target the US market.
Exhibitions and conferences provider ITE (ITE) fell into negative territory following a downbeat trading update, which revealed a continuation of difficult market conditions.
Antiques dealer Stanley Gibbons (SGI) slumped 14.4% to 11.13p on disappointing full year results showing a swing into the red and a suspension of the dividend. Chairman Harry Wilson reported a 43% reduction in net assets due to restating prior years' results and writing down the value of its acquisition Noble Investments and capitalised IT costs concerning the development of online platform The Marketplace.
Kodal Minerals (KOD) undertook a heavily-discounted placing by issuing new stock at 0.1p each to raise £750,000 to advance its lithium exploration project.
Flooring industry consolidator Victoria (VCP) rose 4.3% to 341p following the £13m acquisition of UK underlay manufacturer Ezi Floor.