Britain's blue chip index plunged over 2% at the mid-day point as the realisation sank in in the investment world that the EU referendum may not just be a one horse race.
Financial stocks took the brunt of selling as the Footsie tanked 2.04%, or 127 points to 6,104.
Barclays (LON:BARC) was among top losers as shares shed almost 4% at 169.10p.
Recent polls have increasingly shown the 'leave' campaign gaining ground, which is sending shock waves through the financial world, here and around the world.
"It is clear that there has been a big shift in sentiment around the Brexit over the past 10 days, with poll after poll proving that perhaps it will not be such a one sided affair as many presumed,” said IG market analyst Joshua Mahoney.
Meanwhile, in an interview leaked to the Guardian, the German finance minister suggested Britain was dreaming if it thinks somehow it can still be part of the single market without being part of the EU.
Not helping matters was a slide in the price of Brent crude, which lost 0.46% to US$51.95, and a latest industry report, which showed that by the end of the year, 120,000 jobs will be no more in the UK due to the low cost of oil. Adding to the mix was uncertainty over US interest rate rises.
In small caps, Africa focused carrier Fastjet (LON:FJET) was among the top risers, adding over 42% to 42p as yesterday it was revealed it had nabbed the boss of one of its rivals to become its new chief executive.
Nico Bezuidenhout will take up his new job on August 1 , having been in charge of South African Airways' low cost carrier Mango for the past ten years.
Over that time, Mango has grown from a start-up to a 25% share of the South African domestic market with the lowest unit costs of any carrier operating in the market.
Also up was junior oiler Oilex Ltd (LON:OEX), up 12% to 0.70p as it named its new finance chief and secretary Mark Bolton.
In small cap markets, stocks were also down, with the FTSE AIM100 down 0.7% to 3,481 and the FTSEAIM All share down 0.48% to 740.160.
Weak overseas markets, softer oil prices and the omnipresent fear of burgeoning support for Britain’s exit from the European Union was weighing on sentiment.
The FTSE 100 at 9.30am was off 1.2%, or 75 points at 6,157.
Banks were prominent among the fallers with Standard Chartered PLC (LON:STAN), down 2.2%, the hardest hit.
Supermarket chain Tesco PLC (LON:TSCO) was down 1.8% at 155p after confirming the proposed sale of its 95.5% controlling stake in the Kipa business in Turkey to Migros. The disposal will result in estimated cash proceeds of around £30mln, contributing to a reduction of around £110mln in total indebtedness.
The group’s slightly puzzling expansion into the restaurant market is also set to be unwound, with the group agreeing to sell the Giraffe restaurant chain to Boparan Restaurants Holdings.
Just two FTSE 100 stocks were in the blue: broker Hargreaves Lansdown PLC (LON:HL. and silver miner Fresnillo PLC (LON:FRES).
London’s junior market was holding up a bit better, with the FTSE Aim 100 index down 19 points, or 0.5%, at 3,467. The broader-based FTSE Aim All-Share was 2.6 points (0.3%) softer at 741.6.
Metminco Limited (LON:MNC) was London’s best performer, up 43% at 0.265p. Trading in the dual-listed company’s shares has been suspended down under pending an announcement. The company is anticipating being in a position to advise the outcome of the Los Calatos partnership process negotiations.
Big data specialist WANdisco PLC (LON:WAND) was making a big noise after launching a share placing to raise around US$15mln.
It plans to sell some 6.46mln new shares in the company at a price of 160p each, a slight premium to Thursday’s closing price. The new shares will represent around 17% of WANdisco’s enlarged share capital.
The worst performing stock in London was Frontera Resources Corporation (LON:FRR), the oil & gas exploration & production company. The shares shed 31% as the company called on shareholders to approve various transactions that will result in more shares being issued.
Sector peer Highlands Natural Resources Plc (LON:HNR) was also down in the dumps, siding 10.78p to 52.35p as it announced a test of its re-fracking technology will take place in the next three months.
It is working with the oil services giant Schlumberger to prove the huge potential of the DT Ultravert system.
Retail and hospitality services-focused software company Eagle Eye Solutions Group PLC (LON:EYE) dipped 9.6% to 165p after a disappointing trading update that confirmed revenue for the financial year just ended was lower than management had previously expected.
Early Snapsot
London’s FTSE 100 is set to end the week on the back foot, falling 37 points or 0.59% to 6,196 in early deals.
It comes amid growing concerns over the economic health of the world economy, and follows Wall Street and Asian equities lower.
Financial services stocks topped the FTSE 100 losers board. Standard Life PLC (LON:SL.) was fell furthest in the first half hour, losing 2.27% to change hands at 323.1p.
Royal Bank of Scotland PLC (LON:RBS), Barclays (LON:BARC) and Prudential (LON:PRU) followed, all down about 1.5%, similarly stock broking firm Hargreaves Lansdown (LON:HL.) was also falling.
Budget airline easyJet (LON:EZJ) was another notable name in the column, down 1,6% to 1,465p.
There were only three of the FTSE’s 100 stocks in positive territory, none were up more than 0.1%.