I was locked out of internet banking for my business account with Lloyds for over 3 months due to a technical fault in the way it was setup. Was paid compensation in the end, but already had moved to another bank. They could not have cared less.
Some people will say no smoke without fire, but if you read on moneysavingexpert about people being locked out of their personal accounts for the same reason. Any transfer that is slightly different from your day to day will be flagged and risk having your account locked for weeks / months on end.
It happens more than we realise. A bit like winning the lottery, it could be you :(
The further we go down the road of electronic payments, and a cashless society it could get really messy.
The only way to solve in the short term is to spread the risk across many banks, and never keep your money in one place. Keep hold of some cash!