The shares were bought as part of the abortive bid for Lasmo by Enterprise Oil, a Warburg client.
In a preliminary ruling, first disclosed by the Independent on Sunday last week, the Stock Exchange has upheld a complaint by Swiss Bank that it was unfairly prevented from cashing in its Lasmo shares in the raid.
However, the two sides are attempting to bury the hatchet with a private deal that would obviate the need for a public ruling by the London Stock Exchange.
'The Exchange has made it clear that they would like the two member firms to sort out this matter in a grown-up way,' a Warburg spokesman said.
Swiss Bank is believed to be claiming about pounds 1m compensation from Warburg for not executing a sell order for 3 million Lasmo shares, despite pre-placing the order with Warburg ahead of the raid.
Under the City's takeover rules, Enterprise was allowed to buy up to 10 per cent in its target for cash in the market.
Swiss Bank and other investors claim they were ignored unfairly in favour of institutions supportingthe bid.
Meanwhile, Graham Hearne is coming under increasing pressure from a substantial number of City institutions to split his role as chairman and chief executive of Enterprise.
The institutions have been disenchanted by his handling of the bid and want to appoint a leading City figure as chairman to curb his dominance.
However, Mr Hearne wants to hang on to the top job, preferring to appoint a chief executive at some stage in the next two years.Reuse content