Formed in 2014 and accessible online, via an app and through a UK call centre, Tandem received its banking license in November last year and opened its first handful of accounts in October.

The next wave of prospective customers from the putative bank's waiting list are now being contacted by e-mail and invited to sign up.

The Tandem Co-Founder Community include members of the general public who get exclusive access to new products in exchange for feedback and closer engagement with the bank.

Once onboard, they will be able to trial the Tandem app and open a savings account.

Credit cards, loans and current accounts will be rolled out throughout 2017.

Tandem joins a long list of new banking startups hoping to disrupt the hegemony of Britain's biggest banks by using mobile and online services to forge a new relationship with customers.

Ruth Handcock, Tandem chief customer officer says: “There is a palpable sense that change is needed in the consumer banking sector. Tandem welcomes the challenge and will address the real needs that face millions; helping them plan for the unexpected, helping them get to the end of the month and ultimately making more of their money.”

Tandem is being joined by another new arrival on the UK banking scene in the shape of Loot. The mobile financial services startup has just closed a further £2.5m funding round and intends to open to a 20,000 strong waiting list of prospective customers next week.

Unlike rival challengers. Loot is eschewing the large capital and regulatory risks that stem from authorisation with the FCA, by first building up a loyal user base before approaching the regulator.

Loot provides a mobile banking app connected to a prepaid, contactless ‘MasterCard’ debit card. Each customer has their own Loot account number and sort code, and the underlying e-banking services and license is provided by Germany's Wirecard Card.

“By automatically categorising all of your spending, as it happens, and showing you how much you still have available to spend to stay on budget, Loot puts you totally in control of your money," says Ollie Purdue, founder and CEO of Loot "We will soon be adding a further unique feature, again making use of your spending data, to help you save more money. We will send you messages on your phone offering you special discounts and deals from our partner retailers, cafes, cinemas etc."

The Loot Advisory Board includes Zopa co-founder James Alexander,, VC Nick Kingsbury, John Sills, a former head of customer innovation at HSBC, digital banking consultant Jean-Stéphane Gourévitch Stefan Klestil from investor SpeedInvest.