Swiss Bank Corporation, the investment bank, was fined a total £480,000 sterling (£522.421) yesterday by a London financial regulator for two instances of improper conduct.

The bank was severely reprimanded by the Securities and Futures Authority and fined £300,000 sterling, the largest fine ever imposed by the regulator, for failing to observe the correct procedures during share transactions in UK regional electricity companies almost three years ago.

These transactions were carried out by the investment banking division of SBC before the bank acquired SG Warburg in 1995. Rival investment banks suggested its purchase of shares in Yorkshire Electricity could be linked to the bid for Northern Electric by Trafalgar House, which it was advising. SBC was also fined £180,000 sterling for its actions during the liquidation of Kleinwort European Privatisation Investment Trust (KEPIT) earlier this year and ordered to pay total costs of £176,095 sterling.

Mr Richard Farrant, SFA chief executive, said: "Managing and controlling the different parts of an integrated investment house in order to ensure fair treatment of clients and other market participants is challenging. SBC failed the test."

Mr Farrant said SBC had allowed its market makers to build up an 8.2 per cent stake in Yorkshire Electricity after the traders had rightly guessed the bank's corporate finance department was working with a client interested in making a bid for Yorkshire.