If a loan is being serviced then it shouldn't be possible for a bank just to randomly demand repayment, jack up the interest rate, or otherwise change the terms of the loan. That seems grossly unfair.
If this is the standard in the UK, then I think we need legislation.
The bank calls in the overdraft because of the bank's bottom line, rather than for anything related to the business itself or change in profitability. Was quite common in both the 08 and 91 recessions.
[1] http://www.inc.com/magazine/20100601/why-i-sold-zappos.html
If you owe your bank a million, you have a problem. If you owe your bank a billion, it has.
(Kenyes?)
The essence is that you have to be big enough and have borrowed enough so that the credit losses hurts the bank if they turn on you... But I doubt it's a winning strategy for a small family business.
With the general public they were known as the 'Nederlandse Meeneem Bank' (Dutch takeaway bank) because one of their strategies was to suddenly ask for the whole principal back in one go (something very few businesses can afford, and as your bank they'll know exactly when you can and when you can't) and if you didn't pay up immediately they'd buy up your assets in the bankruptcy proceedings that would immediately follow.
After selling off enough of the assets to satisfy the principal they'd sell off the remainder to friendly parties in order to make an easy profit.
Very nasty practice.
Don't ever put yourself in a position where you are dependent on a single bank, if you need an 'x' amount try to split 'x' across multiple loan providers if you can (it's not always possible, for instance with mortgages).
For a business to have only a single banking relationship is an un-necessary risk.