If you have a Pace Series 4000 STB you should be OK.
However, the Pace 1000 and 2000 series of STB's all use an IRDA frequency, used more commonly for the exchange of information between things like mobile phones and laptop computers by infra red. Their excuse for this is that it has something to do with the use of 'interactive' experience, despite NTL never offering any substantial interactive services. These frequencies are far higher than normal IR remotes, and outside the frequency range of both most universal remotes and video senders.
At this time, apart from the genuine remote control, there is only one piece of equipment which is able to reproduce the correct signal to these boxes - the digital cable 'dongle' adaptor as used with the Tivo personal recorder.
There are companies working on this problem, but their solutions will be expensive and the Pronto is not likely to qualify as one. Unless you have any plans to get a Tivo, you're stuck.