Bookmakers were nursing hefty losses after a cross-party group of MPs called for a clampdown on betting machines that allow punters to lose £300 a minute.
The parliamentary group said the Government should cut maximum stakes on fixed-odd betting terminals from £100 a spin to £2 and slow down the speed at which they operate.
The intervention caused William Hill to sink more than six per cent, or 18.8p to 292.7p, while Ladbrokes Coral dropped two per cent, or 3.5p to 123.6p.
The FTSE 100 Index paused for breath following a heady rise in the previous session, climbing 29.32 points to 6,931.55.
London's top-flight reached its highest level on Wednesday since Donald Trump's shock US presidential victory, adding more than £30 billion to the value of the UK's blue-chip giants.
It came after the market enjoyed a triple tonic of rallying mining stocks, the plunging pound and hopes that Italy may take a controlling stake in troubled banking giant Monte dei Paschi di Siena.
Across Europe, Germany's Dax was 1.8 per cent higher and the Cac 40 in France rose 0.9 per cent.
On the currency markets, the pound was down 0.4 per cent against the US dollar at 1.257, with the greenback strengthening on news that fewer Americans signed up for unemployment benefits last week.
However, sterling was 0.8 per cent ahead versus the euro at 1.183 after the European Central Bank (ECB) poured another half-trillion euro in newly printed money into the eurozone economy to support its recovery.
The price of oil rose 0.7 per cent to $53.35 (£42.42) a barrel despite concerns that Opec's landmark deal to support prices might turn out to be a damp squib.
In UK stocks, shares in Capita plunged to a 10-year low after the outsourcing firm warned over profits and moved to shore up its balance sheet by selling assets.
The FTSE 100 firm said "near-term headwinds", which had pegged back its performance this year, would now persist into the first half of 2017.
It said underlying pre-tax profits, excluding restructuring costs, would reach around £515 million for the full-year, compared to previous forecasts of between £535m and £555m.
Shares were down more than 13 per cent, or 78.7p to 485.3p,
Sports Direct was the biggest faller on the FTSE 250 after profits took a hammering following the collapse in sterling.
Shares dropped more than eight per cent, or 26.10p, to 288.8p after the scandal-hit retailer said underlying earnings plunged 33.5 per cent to £145.3m in the first half of the year.
Nevertheless, the firm said it will still take delivery of a corporate plane in the coming weeks at a cost of £40m.
The biggest risers on the FTSE 100 Index were WPP up 76p to 1,723p, TUI up 35p to 1,099p, International Consolidated Airlines Group up 13.8p to 448.5p, and Polymetal International up 23p to 777p.
The biggest fallers were Capita down 78.7p to 485.3p, Standard Chartered down 18.3p to 666.4p, Royal Mail down 10.9p to 462.1p, and Babcock International down 20p to 938p.
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