Possibly the STB's output channel is set differently from your last box, and is clashing with the DVD or VCR. It should be either 50 or 52 in Brighton. See
http://www.cableforum.co.uk/forum/article.php?a=24 for instructions on checking/changing it. Don't forget to retune your TVs afterwards.
You might need to retune the DVD and/or VCR too. To find out whether they are the problem, remove them from the chain and get it all working just with the ntl box. Then add them one at a time, and see whether anything's broken.