There are two main picture formats for TV - 16:9 (Widescreen) and 4:3 (Fullscreen).
Digital TV, of course, supports both of these. However, analogue can only support one, and so naturally supports 4:3, as most people have this sort of TV.
This posed a problem for the BBC et al - when screening a widescreen show, everything important (including text) must be "fullscreen safe" - that is, viewable by people watching on analogue.
This is, of course, very restrictive, as there is then a large portion of the screen that cannot be utilised. In order to reduce this effect, they began broadcasting widescreen programs in 14:9 on analogue (somewhere in between 16:9 and 4:3), giving small black bars at the top and bottom. This allowed for more of the screen to be used for text.
This brings us to your problem. You must be watching widescreen programs in 4:3 mode, where the sides are simply cropped. As I said above, programs are no longer made 4:3 safe, they are now all made 14:9 safe (with the exception of sports). This may cause small amounts of text to be lost for people viewing in 4:3.
The only solution available to you is to use 16:9 letterbox mode, or buy a widescreen TV and use proper 16:9 mode. If ntl could implement a 14:9 option for digital TV, that would work, but there may be technical issues preventing this.
Hope that helps