The founder of app-only bank Atom, Anthony Thomson, has announced his resignation as chairman.

Thomson has held the role of chairman since Atom was established in 2014. He has guided the business through the process of gaining a banking licence, raising over £250m of capital and becoming one of the fastest-growing start-up businesses in the UK.

Bridget Rosewell, who is the chair of Atom's audit committee, has been appointed as his replacement subject to regulatory approval.

Thomson said he remains "fully committed" to Atom's success and will remain as a shareholder.

However, he added that the "time is right" for him to step down from the role of chairman as the bank "moves into a new phase of development".

"Since having the idea for Atom bank in early 2012 it has gone from being a big idea disguised as a small bank to a big idea and a big bank," Thomson said.

"I am immensely proud that Atom bank has now completed over £1bn of lending to households and small businesses. This is a testament to the efforts of every person at Atom bank, and to the support of all of our shareholders.

"Looking ahead, I have recently co-authored a book on the marketing of money that comes out in March. As I discuss the messages and learning in the book I am going to spend much of the next twelve months travelling extensively. However the people who work at and support Atom bank will never be far from my thoughts."

Bridget Rosewell added: "It is thanks to Anthony's vigour and dedication that Atom bank is what it is today. Anthony is the consumer’s champion, leading from the front to bring true competition to the industry and to change banking for good.

"It is with regret but also great admiration that the Board have accepted his resignation, and I and my colleagues fully understand his reasons for leaving having brought the business to maturity and achieved so much so quickly.

"Today there are 300 people working for Atom bank who will miss Anthony’s unique wit and wisdom, but customers and stakeholders should know that he leaves the bank in great heart and with an exciting future in prospect."