Update;
Bought a new vcr today, one with 2 scarts.
Wired the whole lot together as per wiring diagram in stb manual and all is ok.
The new vcr has the function of disabling the rf output when using scart connections, so I did this to try to avoid further problems.
I guess my problems were being caused by interference between the stb and vcr, and this was exascerbated by the vcr being short on connections.
Having altered the rf channel on the stb, I guess I'll just leave it as everything is functioning ok.
Thanks for all your comments, this forum has been a good find
