Its investigation shouldn't take too long. All MPs need do is look at the big banks' websites, and the evidence is staring them in the face.

The most important number to any bank boss is the net interest margin – the difference between what they pay savers and charge borrowers.

When interest rates were near zero, these margins were squeezed, but with every rate hike bankers take the opportunity to widen them.

In March, NatWest chief executive Dame Alison Rose admitted it made 14 times more from its savers last year than in 2021, with net revenues jumping from £80million to more than £1billion.

The other banks are keeping quiet.

Fran Boait, co-executive director of Positive Money, says the banks are the only beneficiaries from the latest BoE rate hike.

"They not only siphon off those higher interest payments from consumers, but gain billions from the higher interest payments the BoE pays them for the money they hold with it."

Laura Suter, head of personal finance at AJ Bell, urged savers to shift their money as banks "stubbornly" refuse to raise rates. “Someone with £10,000 earning just one percent could earn £271 a year in extra interest by shifting to an easy account paying 3.70 percent, for just ten minutes’ work.”

The big greedy banks won't change their spots, no matter how many letters MPs write. All savers can do is change their bank. They should start today.