Bromley network STBs (like the one you have) do not use standard remote control frequencies (a decision going back long before NTL took control). They signals they use are similar, but not identical to, the IrDA protocol used by laptops and PDAs.
Basically, there are two ways around it. Use an expensive learning remote which can accept IrDA frequencies, or go to
www.redeyeremote.co.uk and purchase a device what can translate standard IR commands into the format used by CWC boxes.