The two groups ended up as the two biggest fallers in the FTSE-250 due to a number of last-minute deals executed below the going price.
The trades are believed to have been part of a big programme order from a large institution and were not a deliberate attempt to manipulate the closing price.
However, they could have a major impact on Misys' chances to return to the FTSE-100. The information technology company, valued at over pounds 3.6bn, is a strong candidate to be included in the top index after next week's reshuffle.
However, yesterday's 4 per cent-plus slump could put paid to Misys' dreams of blue-chip glory. The stock had been bobbing along at around 630p for most of the day when two trades, or a few thousands shares, at 600p were pushed through in the four minutes before the closing bell.
The downward effect of the rogue-ish deals was somewhat cushioned by the recently introduced Stock Exchange rules on closing prices. Under the new set-up, the authorities calculate the final price by averaging out the deals executed in the last 10 minutes. But Misys still lost 26.25p to 617.5p.
To add insult to injury, the software group admitted it had made a mistake in an announcement on a share sale by the executive chairman, Kevin Lomax.
He was previously reported as having netted pounds 120m on the sale, while the real profit is just pounds 1.2m. The reason? Misys mistakenly said that Mr Lomax had sold stock for pounds 605.77 instead of 605.77p.
Back to the suspect deals - RMC crumbled 28p to 705.5p after several trades at 670-689p, well below the 725p going price.
The rest of the market had a solid session with the FTSE 100 finishing 53.1 points higher at 6101.4. Leading stocks were emboldened by a roaring opening on Wall Street, which was showing a triple-digit advance when London closed.
The undercard continued its winning run, with the FTSE 250 closing up 27.9 to 5314.8 and the small cap ending 6.9 higher at 2289.4.
The oil stocks were the stars of the session. After much battering and bruising at the hands of the depressed oil price, the drillers took comfort by the overnight rise in the Brent oil price.
There is a growing feeling that after months in the doldrums, the price could rally as producers contemplate price cuts. Shell, one of longest- suffering oil stocks, rose 18.75p to 349.5p. Its goliath rival BP Amoco was close behind, surging 45p to 902, as Lehman selected as its top oil pick for 1999.
The exploration companies were also buoyant, as renewed bid speculation mixed with the oil price optimism. British Borneo, said to be stalked by a US predator, rose 10p to 115p. Premier Oil put on 1.25p to 11.75p amid vague takeover talk and a Williams de Broe `buy" advice.
Enterprise drilled a 16.25p advance to 288p, supported by a Henderson Crosthwaite note, while Lasmo surged 7p to 129.75p. The two are in merger talks and developments are expected next week.
JKX Oil & Gas completed the party with a 1.75p rise to 8.5p on hopes that the Swiss group National Petroleum might increase its stake from its current 20.2 per cent.
Bid whispers spurred the chemical minnow Albright & Wilson to a 14p rise to 109p. There is talk of an imminent offer at 125p-130p a share from a foreign bidder. Rhodia, FMC, Solutia and a Moroccan company, OCP, were all mentioned.
Among the blue chips, the insurer Royal & SunAlliance shone with a 36.75p increase to 587.75p after good results and a pounds 750m cash return pledge.
Williams, the security and fire group, burnt 16.75p to 348.5p due to disappointing results and worries over a possible exit from the FTSE 100.
Powergen's results lacked energy and the generator's shares dipped 19.5p to 767.5p, dragging down National Power, 15.5p lower at 487p, and Scottish Power, 18.5p worse off at 581.5p.
Dealers turned off BSkyB amid rumours that it was bidding "adieu" to talks with the French rival Canal Plus. The satellite television operator shares crashed 13.5p to 550.5p.
Rolls-Royce's figures were good but not brilliant, sending the stock down 2.75p to 272.25p. Some houses advised a switch into British Aerospace, up 4p to 398.5p, amid renewed talk of a defence link-up with Thomson, the French aerospace group.
The tiddlers risers' table was dominated by Tadpole Technology, up 4p to 13.75p. The electronic equipment maker is set to launch a new product and some major contracts could be on the way.
Aegis attracted institutional interest following its recent results. The media agency put on 1.25p to 130.5p on massive volume of 14.4 million.
Infobank, an e-commerce company, soared 3.5p to 70.5p after securing a lucrative internet deal with the Stationery Office.
Athlone Extrusions, an Irish maker of chemical materials for the car and construction industry, shed 5.5p to 50p after warning of lower profits in the first half.
Voss Net, a member of the buoyant Internet band, logged in an 8p rise to 75p after promising to provide free on-line access to charities.
Recognition Systems Group rose 3p to 17.5p after announcing three important contracts for its customer relationship management.
Durlacher, the broker, soared 25p to 950p, amid mounting bid speculation. Computerland, the computer group, continued to reel from its recent profit warning, shedding 11.5p to 89p.
SEAQ VOLUME: 1.14 billion
SEAQ TRADES: 79,413
GILTS INDEX: 112.01 +0.24
HENRY COOKE, a Manchester-based stockbroker, yesterday put an end to its 113-year long history as an independent company. The broker, founded in 1866, was bought for pounds 20m by Brown, Shipley, the London subsidiary of Credit Bank of Luxembourg. The deal will see the withdrawal of Henry Cooke from Ofex. The firm was one of the original constituents of the unregulated market and yesterday bid farewell at 130p, unchanged on the day.
DELTRON ELECTRONICS, unchanged at 100p yesterday, will today receive a fillip from one its directors. Francois Feldman was set to receive an pounds 800,000 cash payout following the electronic equipment group's purchase of a French rival, EUROiNDustrie. However, he is now expected to take only pounds 538,000 in cash and the remaining pounds 262,000 in Deltronics shares to take advantage of the company's depressed share price.