Macquarie Bank, whose UK investments range from BBC Broadcast to the M6 Toll Road, is believed to have teamed up with software firm Computershare for its bid campaign.

An approach would be the third received by the London Stock Exchange this year and threatens to disrupt the plans of pan- European exchange Euronext, which is awaiting the final outcome of a Competition Commission inquiry into its interest.

Macquarie revealed two months ago that it was considering a takeover bid, but stressed that it wanted to find a partner before approaching the LSE board.

It is understood that this search brought it together with fellow Antipodean firm Computershare, which is best known in the UK for its share registry services and has offices in London, Bristol and Edinburgh.

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