The shares fell 46.5p at one time, closing 33.5p lower at 971.5p. The rumours suggested heavy losses on currency deals in the Far East following the devaluation of Thailand's baht. But a Standard spokesman denied the bank had suffered baht losses.
Footsie ended a lacklustre session down 11.4 points at 4,851.5. Granada, up 28.5p to 812.5p, was the best performing blue chip, spurred by enthusiastic comments from Dresdner Kleinwort Benson and Lehman Brothers.
Centrica continued to score from the Panmure Gordon push, up 2.75p to 89.25p and Mercury Asset Management's comeback kept on course with the shares 42p higher at 1,380p.
The Grand Metropolitan and Guinness merger cocktail became even more confusing with the two rejecting LVMH's proposals but leaving the way open for further talks. The response left GrandMet 10p lower at 609p and Guinness 1.5p off at 597p.
Commercial Union, the insurer, hardened 17.5p to 700p with Salomon Brothers moving from hold to buy.
Elsewhere Psion provided further evidence the market does not take prisoners. Once a high flyer disappoints its reaction is decisive, even cruel.
For a long while Psion, the hand-held computer group, mesmerised the market, evolving as the latest glamour stock of the often tormented British computer industry.
The shares arrived on the old USM in March, 1988, at 97p. Early years were difficult and they hit a 13p low in 1991. But from then on it was heady progress - until last month when the shares peaked at 509p. Yesterday they fell a further 26.5p 313p.
That frequent interruption to a share's progress - a profit warning - caused the damage. In June chairman and creator David Potter launched his new Series 5 machines to critical acclaim. Unfortunately, the celebrations were somewhat muted as he felt obliged to issue a profit warning.
It seems retailers, already overstocked with the Series 3 model, had slashed orders until they could get the new computers. Inevitably, the strong pound was a further damaging influence.
Last year Psion made profits of pounds 16m. The warning prompted forecasts for this year to be slashed from pounds 24m to nearer pounds 16.5m.
When it was still regarded as a dashing, go-ahead company Psion attempted to take over Amstrad. Following its reorganisation Amstrad shares are now, at 278.5p, trading around their highest for six years. They are due to be suspended on Tuesday. Assuming the reconstruction is approved, shares of Viglen Technology, its successor, will start trading on 4 August.
Christian Salvesen, the distribution and storage group, added 22p to 319.5p on suggestions bigger rival Hays would renew takeover hostilities. Hays, which walked away last year, fell 11.5p to 564.5p. Sources close to the company said it did not plan to mount another takeover.
Johnson Matthey, the metals group, rose 5.5p to 570p after JCI, the South African group, appeared to place around 19 million shares at 560p. Cortworth, an engineer, advanced 36.5p after BI, a Kuwaiti group, made an agreed 196p a share offer.
Trading warnings took their toll. Utilitec, a water treatment company, leaked 26.5p lower to 47.5p after producing yet another grim trading statement and Hozelock, the garden equipment group blamed June's downpours for washing out sales.
With sterling also having an impact it said profits would be lower than expected, prompting HSBC to lower its forecast by 38 per cent to pounds 6.5m. The shares fell 78p to 280p. Paper maker James Cropper, complaining of difficult times, gave up 26.5p to 315p.
Biocompatibles International, weak recently on worries over its proposed licensing deal with US giant Johnson & Johnson, rallied 125p to 1,105p; Merrill Lynch was thought to be making positive noises.
VideoLogic rose 6p to 53p on hopes it is winning the race to supply virtual reality technology to Sega's new generation of video games. Trocadero pulled out of its long decline with the appointment of John Conlan, ex- First Leisure Corporation, as chairman. The shares rose 5.75p to 24p.
Struggling Dalkeith Inns is selling its nine pubs to Inntrepreneur for pounds 1.65m. After debts, its assets are expected to be pounds 1.l5m cash - 24p a share. The shares edged ahead to 19p. As a cash shell, shares of Dalkeith, an old plantation company, will probably be suspended.
Bruntcliffe Aggregates, which has admitted a takeover approach, put on 4.5p to 38p as Ennstone, the old Albrighton, emerged as a likely predator. It has acquired, for around 40p in cash and shares, the 9.37 per cent Bruntcliffe stake held by Bodfari Quarries, an unquoted Welsh group. Aggregate Industries is Bruntcliffe's biggest shareholder with 23 or possibly 27 per cent. Ennstone shares shaded to 3.25p.
Compco Holdings, a property group, appears to be adopting a more positive profile. It recently met four institutions and Credit Lyonnais Laing and Albert E Sharp are keen on the group. Stronger institutional support is demonstrated by Equitable Life increasing its stake. Sharp expects profits this year up more than pounds 1m at pounds 3.95m. The shares are 162.5p.