On Friday one of the biggest punts on the direction of shares - alleged to be around pounds 1.5bn - is due to expire. The option has come dramatically unstuck; it banked on Footsie being at 4,300 points.
The contract was taken out in November. With Footsie romping ahead it has been getting seriously out of the money for nearly two months.
It would, therefore, be surprising if the investment house involved, rumoured to be a major institution, has not already taken evasive action.
Even so there are fears it could be forced into dumping some shares and there was talk yesterday of large lines on offer. The position could be made worse by other recent options and futures activity.
Many speculators, banking on a sharp Footsie correction, rolled over short-term contracts. It could all add up to a vicious squeeze and Friday's expiry could be one of the most turbulent sessions witnessed for a long while.
Budget and expiry fears, plus the continuing fall-out from National Westminster Bank, took Footsie down 62.9 points to 4,682.2. It has lost just over 100 points from Friday's record high - not a big fall but it has created worries that the market is in for a sweaty, uncertain summer, even if the Budget is not as fearsome as some expect.
Many strategists predicted a degree of Budget uncertainty would take the shine from Footsie. The general view that the index is heading for 5,000 remains unaltered.
Although Footsie's recent upsurge left the rest of the market floundering in its wake its sudden display of weakness has gripped supporting shares with the FTSE 250 index and the FTSE SmallCap index giving ground.
There was, however, no deluge of selling. Turnover remained around average with Norwich Union, down 6p at 318.5p, attracting a 40 million-plus volume.
NatWest slipped a further 9.5p to 745.5p and would have gone lower if some absurd story of a takeover bid had not been heard.
Even so, the accident-prone bank helped unsettle the rest of the banking sector with Abbey National off 37p at 831p and Lloyds TSB 20p at 606.5p.
Grand Metropolitan and Guinness were the toast of Goldman Sachs, which suggested prices of 660p for the two merger hopefuls. LVMH, the French group which opposes the deal, barged in by cheekily buying 4,750,000 GrandMet shares at an average price of 577p. It said it had no intention of bidding for GrandMet, up 15.5p to 581p; Guinness rose 8.5p to 588.5p.
Engineer Siebe, as its takeover of APV drew towards its close, gained 18.5p to 988.5p.
Midland Independent Newspapers, the Birmingham Post group, rose 30p to 179p as it disclosed it was in takeover talks with Mirror Group, off 3.5p to 205p.
BSkyB tumbled 21.5p to 566.5p as chief executive Sam Chisholm said he would leave at the end of the year. Some suggested the Chisholm factor was worth 100p a share.
EMI, the showbiz group, picked up 120,000 shares at 1,170p. It is returning nearly pounds 500m to shareholders through the creation of "B" shares, worth 114.5p, which can be redeemed shortly after they are issued.
Carpetright rose 37.5p to 478.5p on its results, dragging MFI Furniture 7p better at 142p. British Vita, the chemical group, edged ahead a further 3.5p to 219p amid talk BZW had turned positive. The shares were 192p last month.
Bluebird Toys rose 10.5p to 90.5p on hopes of takeover action and Rage Software put on 1.25p to 4.5p after selling a loss-making off-shoot and expressing hopes it will return to profits. Managing director Paul Finnegan purchased 560,000 shares at 3.5p.
Petra Diamonds firmed to 108.5p; it has acquired diamond concessions covering 10,000 square miles in north eastern Angola.
Bakyrchik, the gold hopeful, was suspended at 83.5p as it sought more cash.
Newcomers made sound debuts. Powderject Pharmaceuticals reached 197.5p from a 185p placing and Highland Timber, off a 120p launch, reached 127.5p.
On Ofex, Capolito Roma, a clothing and footwear retailer, rose 4p to 47p. The company has said it is in takeover talks. One rumour is Owen & Robinson, unchanged at 10.5p, will bid 55p a share.