Building Society and other UK accounts automatically have basic rate tax deducted at source - unless the accountholder declares he/she is entitled to have it paid gross, so ignore what is said above.
I suspect HMRC are wondering what you are living on, and that is the reason for the compliance check.
Employing an accountant, whether it costs not very much or not, seems a waste of money if your affairs are that simple.
I'd just go ahead - it seems that you have nothing to hide.