accused of stealing at work

I Have just started working in this shop that sells cards and before my last day I was accused of stealing £40. at the end of every shift we are expected to count the takings that was made and put it in a box which everyone has a key to and that day I finish at 3 and counted up the money as usual and put it in the box and now my co-workers has said that £40 has been missing from the box and they are accusing me of taking it which I did not. and I have no need to steal since im pretty well off and just having a part-time job to waste time. how can I prove that im innocent? I mean anyone could have got into the box after I left since the shop was open untill 9 and that was friday and now is monday and they only told me on monday. something similar happened a few months back but the company couldn’t find who done it since they dont have cctvs in the shop. I am quite happy enough to get the police involved just prove my innocence.