Anne Boden, chief executive of Starling Bank, said that the use of cryptocurrencies by criminals is a challenge for investors and banks.

People are being tricked and the proceeds are usually used to buy things. She said that the assets aren't sustainable in the long term because of the environmental issues they will cause.

In a rare example of a European fintech achieving a value that was double the level of its previous round, Starling last month raised new funds in a round that valued the business at more than 2.5 billion dollars. Early backer Harald McPike and a unit of Goldman Sachs Group Inc. were among the existing investors who participated.

The bank could list in London at the end of the year. She said that the London market is hard on technology companies and loss-making companies.

Starling's future growth will come from selling its technology platform, Engine by Starling, to other businesses that want to offer banking services.

In four to five years, I think we will be a global technology company that owns a bank in the UK.

Big banks around the world have a huge problem, it's not a problem of innovation, it's a problem of cost base, and being stuck on technology that's gone past its sell-by date.

Starling has received queries from other banks about using its technology. Users would need to get a banking license from another party to use it.

Starling was set up by Boden. Small and medium-sized businesses make up 450,000 of the bank's customer accounts. She said that it can no longer be called a challenger bank in the UK.

When asked about takeover approaches from larger rivals, Boden said that Starling is not for sale. The bank is looking at acquisitions.

We must question whether the richest man in the world and his ownership of the streaming platform is something the world really wants.