The other reason for these phone scams is that, with interest rates being so low, there is little point in moving spare cash out of a current account into saving or investment account paying more interest, because there isn't one.
As a result, people are building up huge balances in their current accounts. The best and safest thing to do is limit the amount of money in your current account to one month's salary/pension so that in most cases, if you are scammed the most you are likely to lose is £1,000 - and it could be much less. At the end of each month transfer any excess sum in the account to a savings account.