I'd check it out sooner rather than later.

If the crank is loose on the shaft then yes you stand the chance of damaging the crank arm/s by having it wear away against the shaft.

If all is tight and it's a BB issue then it's certainly not going to get any better onits own.

Halfords sell reasonably priced basic tools like this

http://www.chainreactioncycles.com/Models.aspx?ModelID=7857