F&C Asset Management has approached mergers watchdog, the Takeover Panel, to investigate the stake-building of two of its biggest shareholders, Sherborne and Aviva Investors, reports the Times.

F&C maintains that both the investors, whose combined holdings were over 25 per cent, were acting "in concert", the paper said in its report.

The panel has yet to take a decision on the matter. However, in the event of the Panel ruling in favour of F&C, it could pose a roadblock for Sherborne and Aviva in increasing their holdings in the company.

F&C has strongly resisted Sherborne's attempted coup and condemned it, saying it could bring unwelcome uncertainty. Sherborne currently holds a 17 per cent stake in F&C, which makes it the latter's biggest investor.

Last week, Sherborne attempted to evict F&C's chairman Nick MacAndrew and install American activist Edward Bramson at the head of the fund manager's board as well as bring in two other independent directors.

The move has been supported by Aviva Investors, F&C's third biggest investor with a stake of 8.14 per cent, thus prompting F&C to infer that the two companies were acting in concert.

However, David Lis, head of equities at Aviva, has denied any involvement in the affair.