I had a similar, but different, problem last month - I needed something to convert Coax IN to SCART OUT.
I bought a modulator in Maplins (c. €50). Despite the assurances of the in-store staff and help desk, I could not get it to work, and got a refund.
This could work for you but only for one UHF frequency, i.e. you could be limited to one (Coax) channel.
A more cumbersome alternative would be to buy a VCR - SCART from ntl box to VCR, then Coax from VCR to TV2. This would give you the full spectrum of Coax channels.