It is understood that lawyers are discussing the termination of the contract. Shop, which was formerly Campbell Doyle Dye, and Invesco were unable to make any comment as Campaign went to press.
The account loss will come as a blow to Shop, as it was one of its biggest pieces of business. The agency was hit last year by the consolidation of the Mercedes-Benz business into the BBDO network, after it had worked on the account for six years.
The agency's remaining clients include Green Flag, Christian Aid and Thorntons.
Invesco appointed Shop in February 2006 after a pitch against Miles Calcraft Briginshaw Duffy, Maher Bird Associates and the incumbent, The Gate. The bulk of the activity on the business is in the national press or outdoor, plus some online advertising.
Invesco Perpetual invests in pension funds, ISAs and other products on behalf of consumers and institutions.