Activist investor Olivant is in contact with the administrators of collapsed bank Lehman Brothers to secure its 2.78 per cent stake in UBS, which the fund holds through Lehman, according to a report in the Financial Times.

Olivant, the investment company of former UBS chief executive Luqman Arnold, earlier this year clashed with UBS's new management and called for a separation of the Swiss bank's troubled investment banking business from its profitable wealth management arm.

Olivant said in a statement the stake - worth about $1.34 billion - is held through Lehman Brothers International ( Europe).

"We're in discussion with Lehman to establish the ownership of the shares,"  Mr Arnold was quoted as saying. "We are doing everything we can to recover our position."

The announcement casts doubt on whether Olivant can vote at UBS's extraordinary shareholder meeting today, when the bank will present a restructuring plan announced in August along the lines demanded by Mr Arnold.

The market is only just starting to understand the impact of a prime broker going bankrupt, because no one had ever considered the consequences before, Mr Arnold said.