It looks as if it's been kept in too much shade so it's difficult to tell what it is exactly.
However I would say it is possibly Pachyphytum oviferum.

Here's a link ...
http://www.cactus-art.biz/schede/PACHYPHYTUM/Pachyphytum_oviferum/Pachyphytum_oviferum/Pachyphytum_oviferum.htm

Hi Hywel,
Having looked up the name you mentioned I think that you are correct.
The plant has been in my conservatory and in my shed which has plenty of light.
Thank you for your response.
Iain-p

It should not be stringy like that, as you probably saw from the link. I would try to give it some more sun.