I have had the same problem in the past Newbolt.
Bearing in mind I have a combined DVD/VCR here is how mine is set up.
Scart 1 (on tv) goes to scart marked (tv) 0n digi box.
A second scart runs from the digi box to a scart socket marked VCR in+out DVD out.
The external TV aeriel goes into DVD/VCR combi then back out to TV.
I have a Telewest digi box, this has a single input aeriel type cable from a box outside straight in to the Telewest digi box.
Hope this helps...Fred