Shares in the British advertising group fell early on Friday, when Murria's vehicle AdvancedAdvT (ADVT.L) said a takeover proposal would be in shares, and slipped again when M&C gave its response later in the day to close down more than 12%.

Software entrepreneur Murria owns 13% of AdvancedAdvT, in which private equity group Marwyn is the biggest shareholder. She also owns 12.5% of M&C directly, while AdvancedAdvT owns another 9.8%.

Murria is the deputy chairman of the ad group, which was founded in 1995 by brothers and ad moguls Maurice and Charles Saatchi.

The remaining independent directors said the proposal did not offer an alternative strategy, beyond a change of control.

"Furthermore, the proposal does not reflect the value of the business and its future prospects and would disproportionately transfer equity value from M&C Saatchi shareholders to AdvT shareholders," the ad group said.

Murria's AdvancedAdvT set out its plans for M&C on Friday, a day after the ad group confirmed it had received bid interest.

"We look forward to the opportunity to discuss our proposal and address the points raised in today's statement with the independent committee of M&C," AdvancedAdvT said following the company's response.

AdvancedAdvT, which does not own any other assets, raised 130 million pounds ($176 million) last year. It said a merger with M&C would provide firepower for deals and improve its digital capabilities.

"The combination of the M&C brand and platform with the company's funding and experience is expected to increase the M&A opportunity pipeline," AdvancedAdvT said in a statement.

($1 = 0.7390 pounds)