Blue chip stocks are on course for their worst week since January in afternoon trading , as values plunge due to US election jitters.
Markets around the world were lower as trading was dominated by Donald Trump's resurgence in US presidential election polls this week.
Overnight Japan's Nikkei 225 closed more than 1% lower, while in Europe both Germany's DAX and the Cac 40 in France fell.
In London, the FTSE 100 Index was down 98 points at 6692.6, extending losses from the four previous sessions this week. Top flight shares were almost 1.5% down in this session, wiping almost £25bn ($31bn) off values.
The FTSE 250 Index fell 293.5 points to 17288.4.
Spreadex financial analyst Connor Campbell said: "What started as a few jitters morphed into a full on panic attack this Friday, the European indices plunging at the prospect of Trump moving into the White House."
The FTSE 100 has fared worse than European markets over the past few days because of a partial recovery in the value of the pound linked to a Brexit High Court ruling and the Bank of England's Inflation Report.
Sterling's slump of almost 20% against the dollar since the Brexit vote in June has boosted many of the internationally-focused firms on the FTSE 100 Index who sell in dollars and convert sales to pounds.
But this week's moves by the Bank of England and the courts, has provided the pound with some respite.
Bookmaker's strong Euro 2016
Paddy Power Betfair was the strongest performer in the top flight after the bookmaker lifted its full-year profit forecast, boosted by the weak pound and by strong trading during Euro 2016.
The group said it expects its core earnings to be in a range between £390m and £405m, compared with initial guidance of between £365m and £385m.
In afternoon trading the biggest risers in the FTSE 100 Index were Paddy Power Betfair (+345p to 8925p), Rolls-Royce Holdings (+8p to 715.5p), United Utilities (+9p to 931p), SSE (+11p to 1574p) and National Grid (+1p to 1021.5p).
The biggest fallers in the FTSE 100 Index were Hikma Pharmaceuticals (-106p to 1639p), Dixons Carphone (-14.3p to 327.2p), International Airlines (-18.1p to 432.7p), Persimmon (-66p to 1692p) and Taylor Wimpey (-5.5p to 141.6p).
In afternoon trading the biggest risers in the FTSE 250 Index were Tullett Prebon (+14.4p to 382p), CYBG (+5.4p to 280.3p), P2P Global Investments (+14p to 809p), Aggreko (+12p to 800.5p) and Pennon Group (+9.5p to 814.5p).
The biggest fallers in the FTSE 250 Index were DFS Furniture (-28.7p to 235p), Mitchells & Butlers (-13.6p to 268.6p), Intermediate Capital Group (-29p to 590.5p), Regus (-11.5p to 234.6p) and Crest Nicholson Holdings (-20.2p to 414.7p).