David McCarthy, who resigned in September after eight years as Atom Bank’s finance chief, will assume the same position at Tandem Bank, a smaller competitor.

To speed its expansion in a hard economic environment, a challenger bank specializing in green finance has poached its new finance boss from a rival.

David McCarthy, who resigned in September after eight years as chief financial officer of Atom, is joining Tandem Bank in the same capacity.

The appointment of Mr. McCarthy, which will be disclosed on Monday, is part of Tandem’s effort to strengthen its senior management ranks.

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

Alex Mollart was introduced as the new CEO of Tandem in the fall, while former TSB CEO Paul Pester was appointed chairman earlier in the year.

Pollen Street Capital supports the lender, which purchased Harrods Bank in 2018.

It focuses on capitalizing on the rising demand for green finance with solutions like a recently introduced green mortgage.

In addition, it developed Tandem Marketplace, a hub where consumers can obtain sustainable and energy-efficient products and services, and is a financial partner to several big energy and home renovation companies.

This year, Tandem’s deposit base reportedly surpassed £1 billion, but it remains a modest player in Britain’s enormous retail banking sector.

The business declined to comment on Sunday’s selection of Mr. McCarthy.