Ok so located the source of an annoying rattle, a broken clip fixing the rear seat, no idea how to find a replacement after spending a long time on the internet.

Please does anyone know what this is called and/or how to find a replacement! 

Thanks.

Welcome to the club, James.

I think the best bet to find what the "little white thingy" is called is to find a car breaker  ---  there are several members who can help, and hopefully might even have one.  There is a member The Jag Den who is worth contacting as he does break Jaguars.

If you know a good garage/mechanic you could also struck lucky.

Let us know you you get on.

Regards,

Peter.