I think it depends on the interest you get from the savings rather than than the amount you have got in the bank. i rang last year and they told me to wait for this years'interest thingy to come from the building society. if interest is above a certain amount-see the booklet you get with your form as can't quite remember what the limit is-then you have to declare it. but if i remember rightly, it's quite a large amount of interest you need to have earned on your savings anyway.