I guess it depends what you hope to achieve.
Obviously if it is the return of the goods and he is the type to have sold them then the law is not going to help you.
If you want some form of redress and the goods are valued at less than £5000then a claim through the small claims track of the County Court may be worth persuing. You can do it yourself and it doesn't cost a great deal. I've used the Money Claim Online service without too much trouble/cost (though this has been against businesses for money unpaid. I've no experience of claiming for possession of goods.) Again, it depends on the character of the "defendant" how bothered would he be by the threat of having a CCJ against him?
Just another thought. Have you spoken to your insurance? Your MiL could possibly claim for the loss, and it may be that (as with car insurance) the insurers would seek to claim the expense from the "guilty" party.
(Cave Duck, Mon 19 Jul 2010, 17:30, 1 reply, 16 years ago)

seems to me that you insurance route is probably the most likely to yield results
of all the suggestions on here
( Vipros. clever got me this far, then tricky got me in, Mon 19 Jul 2010, 17:56, Reply)