A challenger bank specialising in green finance has poached its new finance chief from a rival as it seeks to accelerate its growth in a challenging economic environment.

Sky News understands that David McCarthy, who resigned after eight years as chief financial officer of Atom in September, is joining Tandem Bank in the same role.

Mr McCarthy’s appointment, which will be announced on Monday, will come as part of a reinforcement of Tandem’s senior management ranks.

It will also say that Wahid Ali, a former executive at Royal Bank of Scotland and official at the Prudential Regulation Authority, has been recruited as its chief risk officer.

Tandem announced in the autumn that Alex Mollart had been hired as its chief executive, while the former TSB boss Paul Pester was named chairman earlier in the year.

The lender, which acquired Harrods Bank in 2018, is backed by the private equity firm Pollen Street Capital.

Its focus is tapping into the growing demand for green finance through products such as a recently launched green mortgage.

It also launched Tandem Marketplace, a hub for consumers to find sustainable and energy efficient products and services, and is a finance partner to a several major energy and home improvement providers.

Tandem’s deposit base is said to have broken through the £1bn barrier this year, although it remains a tiny player in Britain’s vast retail banking market.

The company declined to comment on Mr McCarthy’s appointment on Sunday.