thanks everyone - I'll try claiming from RM but it sounds like a nightmare!
To be fair I think it's made to sound worse than it is, (of which I'm guilty too

).
It's not so much a nightmare, just a lengthy drawn out process. You can't file a claim with the RM until 15 days after the posting date IIRC, then you've got the maximum claim value, (dictated by the service paid for), and you've got to supply pricing evidence , but I've just printed the
ebay ad off in the past for that.
The RM will probably contact the buyer to have them confirm it hasn't arrived, so it could be worth emailing the buyer and telling them you are making a claim and the RM will be contacting them as part of their 'possible' criminal investigation. You never know, it may just prick their conscience if indeed they have 'tried it on' by saying they've not got it.
You might just get a reply saying, "Er, thanks for you message,
the item actually turned up yesterday / the item was at the depot when I went for something else / I'm a nobber and I did get it really" *
You never know, nothing ventured and all that. The irony I've always found with the RM claim process is they don't refund your postage costs! Never quite fathomed that one out.
Good luck with it regardless.
*delete as appropriate