Well, I suspect that if they have gone to the trouble of making sure that their CLI shows an 0870 number then they can call you back if they really want to talk to you.

Has anyone tried making a transfer change / reverse charge call?

I think that you'll find this is the creeps that phone you & ring off quick, leaving you with the 0870 to ring back on, then keep you on hold for ages to make some money out of you ! 

My brother has had them ring him more than a few times & I told him the same thing as I'll tell you.

If it's that important & they really want you, they'll ring you back, but I think somehow that you'll find that
I think we've had a previous posting about this but searching the Forums I couldn't find it ! If I do find it, I will add the reference link here.

INSIGHT are a supplier of computer goods. I use them. They have an 0800 number to contact them. On the face of it, they do seem a responsible company, so i would be surprised if it is a scam - but then - what do I know ?

Telewest are simply the providers of the number. A batch of numbers is allocated to each provider for them to sell to the end user. Information about the allocations can be found on www.ukphoneinfo.com