Bob Diamond, the former chief executive of Barclays, is staging a City comeback after agreeing to buy one of London’s oldest stockbroking firms.

Diamond’s buyout vehicle, Atlas Merchant Capital, has teamed up with QInvest, the Qatari investment bank. to acquire Panmure Gordon.

The deal marks a return to the Square Mile for an American banker whose high-flying career came to a halt in 2012 when he was forced to quit Barclays in the wake of the Libor rigging scandal. The then chancellor, George Osborne, described Diamond’s resignation as “the right decision for Barclays – and for the country”.

Diamond – once branded the “unacceptable face of banking” by Lord Mandelson – is choosing one of the City’s most venerable names for his comeback. Panmure Gordon was founded in 1876 and its alumni include David Cameron’s late father, Ian, who was a senior partner at the firm.

Panmure directors unanimously recommended the offer of £1 per share, which values the company at £15.5m. Atlas will control a majority stake, with QInvest maintaining its existing 43% stake.

Diamond did not comment in a statement confirming the deal, but Matthew Hansen, boss of Atlas in the UK and Europe, said: “We believe there is significant opportunity for Atlas, in partnership with QInvest, to apply our operational skills and financial services expertise to enhance Panmure Gordon’s strong reputation and build a larger, successful boutique investment bank.

“This long-term stabilisation and development can only realistically be achieved as a private company, out of the glare of the public market and the effects of share price movement.”

Diamond is not expected to have a day-to-day role in the management of Panmure Gordon, with Hansen more directly involved in the deal from Atlas’s side.

A statement from the stockbroker said that its independent directors unanimously consider the offer price to be “fair and reasonable”. The deal requires the backing of a majority of shareholders, representing at least 75% of shares. It has already secured the support of investors owning 60% of its stock.

Before he founded Atlas Merchant Capital, Diamond co-founded Atlas Mara, a London-listed investment vehicle focused on buying financial services businesses in Africa and with operations in seven countries.

Diamond had big ambitions for Atlas Mara, which was part of a consortium that last year expressed interest in buying Barclays’s African operations. Partners in the bid included the US private equity firm Carlyle and Atlas Mara indicated at the time that if the deal went ahead, it would likely be taken over by the consortium. However, the deal appears to have fallen by the wayside after Carlyle reportedly pulled out.

Shares in Atlas Mara have fallen by about 80% since it listed in December 2013, and its chief executive John Vitalo stepped down last month. Vitalo had joined the company in 2014 as its first chief executive.

Last month Atlas Merchant Capital announced its first European investment, teaming up with the ex-chief executive of Greek bank Piraeus to buy the Athens-based consumer finance arm of France’s Crédit Agricole.

