I'm not sure where you're looking, because following your link, it tells you that it's an

0871

which is 10p anytime, which it also mentions in the first paragraph.
Where did you find this 5p/min off peak  ???

Thanks Dan

I'll have to keep an eye out for that small white text in future  !!    

Right, I see that uses a different access number

0844

. No problem - it's definitely cheaper.
Funnily, follow the link below & according to the BT rates, that's 5p

anytime

   Worth checking it out ??
I shall have a test of this and see if it works daytime too and update this post.

Overall at the moment, still comes out on top, equal on daytime rate & better on weekend rate.
I think that I'll stick with for the overall package. I'm starting to look at the feasability of going to PAYG and using the home phone for mobile calls as it's now starting to be the cheaper option.

Does anyone happen to know the 0844 number, as that website seems to be down.

Thanks
Daniel