[keep it simple]

Thanks all for your help.

Firstly, daern :

Get a standard UHF aerial lead and plug it from the RF output of the STB to the socket on the wall where your old terrestrial TV used to come from. (Most people still have these)

The wall socket is only linked to the cable running down the external wall from an old rooftoop aerial which is no longer there! (it blew down in a storm and was never replaced as i now have cable and didn't need it).

Go into the loft and find where the two aerial leads (i.e. the one from the STB in the lounge and the one from the second TV) come out and join 'em up.

No aerial leads in the loft, as far as i know. Main lead runs down external wall, as mentioned above. Only aerial lead to second tv is the one from the downstairs signal booster.


altis:

You will even be able to do fancy stuff like record a cable channel while watching different, terrestrial, ones on the TVs.

yup, can already do all that.

Have compared your modified diagram (with all the unnecessary bits crossed off as you suggest) to my own drawing. No problem with the scart leads . Seems to me the only real difference is i don't have the rf lead from the stb to the vcr. I'm not totally sure why that is a problem, as my incoming cable is split - if i have a direct feed from the cable into the vcr, do i need a feed from the stb to the vcr? or is it something to do with the difference between the raw incoming signal and the decoded signal which i guess comes out of the stb?

MovedGoalPosts seems to have come up with the simplest and most logical suggestion:

Simply disconnect the coaxial aerial out from your video to your booster. Instead run a coaxial from the STB aerial out to the booster and that should be it.

because the booster currently takes its feed from the vcr, that is why the upstairs tv can view whatever is on the stb, but if a video is played then it can only view what the video is playing. If i run a lead from the stb to the booster instead, as suggested, it should solve that problem, i.e. even if a video is played downstairs, the upstairs tv will still be able to see the signal from the stb.

Can someone just confirm that, because the connectors on the stb and booster are different, i need a cable with an rf plug on one end and an rf socket on the other?

Thanks all for being patient with me