Would a bank be within its rights if it came into your house and took the cashbox you keep under the bed? Of course not. I can see no difference between that and the money you have in your current account. The money belongs to you, not to them. Helping themselves to it is just not on, no matter how much you owe them.
Of course banks should do what they can to retrieve money owed to them. Further, I believe if you owe money you should do whatever you can to pay it back. But that shouldn't give banks carte blanche to raid your account.
Look at it this way: if your current account or savings was with another bank than the one you borrowed from, the latter couldn't help themselves to your cash. For that reason it's simple to avoid the right of set-off. Simply have your current account with a different bank or building society than your mortgage or credit card. If we all did that, the potential problem with set-off would disappear at a stroke. Banks can't raid the accounts of people with other banks, no matter how much they might like to.
But why should we be forced to switch accounts or rearrange our finances simply to put a stop to a bit of nonsense from the banks?
They are already in the dock over high charges and bringing the economy to the brink of collapse, and now should be doing everything they can to repair their relationships with us, their customers.
So I'm calling on the banks to do the decent thing and voluntarily give up the right of set-off. They have plenty of other tools in their armoury to get back their money from creditors, so scrapping the right to set-off won't damage them financially. But if the odious practice was ended, it would stop banks adding further money problems to people like Helen Allingham and others who may already be on a financial knife-edge.