The announcement that the Competition and Markets Authority (CMA) has launched a full competition inquiry into current account and small business banking markets, first mooted in July, has come as little surprise.
It will look into the difficulties customers face in switching banks, and the lack of smaller competitors to the "big four" High Street names.
The CMA confirmed it has launched a full inquiry into current accounts because of low levels of switching, limited transparency and barriers to entry.
But, crucially, the CMA says there's been very little movement over time in the market shares of the four largest banks.
The authority also said it would review the 2002 report by its predecessor, the Competition Commission, to see if its findings were still relevant.
Richard Lloyd, Which? executive director, said: "This decision means it's now crunch time for the biggest banks that dominate a market blighted by a lack of trust and poor customer service. We want the Competition and Markets Authority to expose the cost to consumers of a lack of competition in the current account market and to pave the way for reform.
"In the meantime the banks should seize the opportunity to demonstrate that they can put their customers' interests back at the heart of their business, whatever the outcome of this inquiry."
David Mann, head of money at uSwitch.com, said: "This is an important first step towards fixing the many ailments of Britain's broken banking sector.
"True competition is needed to break the big four's oligopoly over our bank accounts. However, the two years that a full investigation is likely to take is too slow and more needs to be done to help consumers in the here and now."
He added: "The iron grip held on the current account market by the big four banks has bred a culture of complacency. Consumers can see virtually no difference between the services offered by different banks."