The last 12 months have resembled a fee Nirvana for dealmakers, yet in these heady times corporate financiers have had to monitor a new set of rules.

The rules could impact on the M&A feast, which has seen a wave of deals including Telefonica's acquisition of O2.

The Takeover Panel has recently closed consultation on a proposed rule that will oblige holders of options or derivatives on company shares to make mandatory bids for these companies.

The Takeover Panel's reasoning is that hedge funds, and the like, have been using derivatives and options to gain stakes in bid targets. In doing so, they have been able to skirt the 30% threshold that requires the holders of ordinary shares to make a mandatory offer for a company.

'If you hold an option or derivative on a stock you have a degree of control over those shares,' said Mark Warham, the director general of the Takeover Panel.

He added: 'If you have an option on 30% of a company's stock then you should have to make a mandatory offer, as the holder of 30% of a company’s shares would.'

The panel is scheduled to release a response statement on the consultation at the end of this month. But sceptics have made it known they disagree with the panel’s reasoning.

In its response to the consultation, the ICAEW's corporate finance faculty, which represents 5,600 dealmakers, said: 'We do not consider that an option holder and a holder of a derivative necessarily has de facto control over the underlying shares'.

It added: 'Derivatives can take a myriad of forms and with many derivatives there is a real lack of transparency as to what action the counterparty may take to hedge its position.'