(Reuters) - M&C Saatchi's top investor said on Friday it would not increase the terms of its takeover offer for the British advertising group, after the company agreed to be bought by consultancy Next Fifteen Communications.

AdvancedAdvT said its offer of 253.6 million pounds ($316.1 million) for M&C from earlier this week was final. Next Fifteen agreed to buy M&C for 310 million pounds.

($1 = 0.8023 pounds)

(Reporting by Sinchita Mitra in Bengaluru; Editing by Shounak Dasgupta)