Ok,please name the 'friendly' to Bitcoin banks in the UK as i'm sure a lot of guys would love to know.me incluided
Probably it has not much to do with Bitcoin at all.
In case of most non-business bank account, the only money coming in are from your employment, with occasional transactions from friends/family, paypal and other known institutions.
So it may be the case, that when you're sending/receiving funds from bitcoin exchange (often foreign bank account) it could trigger the 'suspicious transaction' procedure on the bank's system. This comes with the costs of engaging staff to perform investigation.
Even if they figure that there's nothing illegal about your activity, they could simply estimate that costs of regular investigations on your account exceeds any potential gains. So they'd be better off by simply closing your account.
Although that's just my theory. On the other hand, Bitcoin is not much of a threat to banks atm, but as it's growing, it'll be taking some of the banks' income little-by-little, so it could be their way to try to keep people away from it.