The appointment of Brian Keelan of SBC Warburg came as a group of nearly 50 Labour MPs put down an Early Day Motion denouncing Mr Regan as an "asset stripper".
The motion said: "This house deplores an attempt by asset strippers, hiding behind brass plates in Monte Carlo, the West Indies and the Channel Islands, to seize the assets of the Co-operative Movement which for more than a century has served the best interests of Britain's consumers."
It urged the Bank of England, the DTI and the Stock Exchange to "halt this charade before another scandal in the City emerges".
The motion caused a furore at the House of Commons as six of the 47 signatories were Labour Co-op MPs who failed to record their interest.
The MPs said they had received no backing from the Co-op since 1992 and had not thought there was anything to declare.
The Co-op's appointment of Mr Keelan was taken in the City as a signal that the movement is taking the Lanica Trust approach seriously.
It also forges an odd union between one of the City's most aggressive, red-blooded takeover specialists and a democratic movement founded in the early nineteenth century to improve the conditions of the working man.
Another twist is that it pitches Mr Keelan on the defence side of a "bid" when he usually represents the bidder.
His past battles include representing Trafalgar House in its failed bid for Northern Electric and a failed break-up bid for National Power by the Southern Company of America.
The Co-op denied that Mr Keelan's appointment heralded a takeover bid battle.
"It is not as if we are preparing for a hostile bid. But you need merchant banking advice."
Warburg has provided the Co-op with financial advice since 1964.
Mr Keelan has been recruited to give specific advice on how it should consider the approach by Lanica's associate company, Galileo.
It is thought the Co-op is expecting Lanica to make its move in the next 10 days or disappear from the scene.
Though Lanica has secured backing of pounds 1.5bn and due diligence money of pounds 10m from City institutions such as Schroders and Perpetual, the Co-op is expecting Mr Regan to withdraw from the fray.
Lanica Trust said it was bemused by Mr Keelan's appointment.
"They keep saying the matter is closed. But if that is the case why have they appointed Warburg? It all seems rather odd."
The Co-op maintains that a break-up bid is precluded by the group's structure in which it is owned by its members - the regional societies.
The movement has its roots in Rochdale where a local warehouse became the first Co-op shop in 1934.
It grew to include supermarkets as well as a chain of funeral parlours, travel agencies, opticians and garages.
It owns the Co-operative Bank and the Co-operative Insurance Society.
It has huge farming and milk interests. It also has a manufacturing business which makes safety footwear and shirts.
The Co-op is formed of 51 regional societies, of which the largest are the Co-operative Wholesale Society, which owns the bank, and the insurance business, the Co-operative Insurance Society.
The movement's combined turnover exceeds pounds 7bn.
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