Yup me too, I'd ask the buyer to send the item back first, then if they didn't warn them of impending action before I did it. Tell them what expenses you are likely to claim (the court fee, etc). So they have a chance to do the right thing. The process is easy and so far I haven't lost a case.
It wouldn't matter to me whether it was a few pounds or not, if I wanted to make a point.
PS. the police wouldn't get involved as its a civil matter. You are covered by the DSRs, the buyer is expected to take reasonable care, etc. If you state in your T&Cs that the buyer is expected to return at their own expense (seller refunds the return carriage if its the sellers fault), then the buyer must do so. You can of course arrange to collect the item also.
If you let the buyer get away with both money and item, then they will do this again to someone else.