There is a good site with information on which type of IR system works with ntl STBs, but you do have to visit a few pages and read the text carefully to fully understand it.
http://www.cyberselect.co.uk/range/457
The supplied link is one that has hyperlinks to just about every other page you need to erad to make sure you get the right product, but i have dealt with this company and found them to be very knowledgable if you call them up and ask to speak to a technical advisor so that you get the right thing for you.
Hope this helps.