I'm really sorry to hear that your enjoyment of the rugby has not been the best, and I'd like to ask a few more questions regarding this.
I've done some testing on your set top box, and can't find any issues with signal strength or the hard drive, so could you let me know if the poor picture is only during live sport, or is it at all times?
Do you get the same issue if you try the HD version of ITV4 (channel number 178), or if you are already watching this in HD, is the same issue happening on the SD version (Channel number 118)
How does the poor picture manifest itself? (e.g. is it Freezing, blured etc?)
And finally, do you notice this issue on any other channels at all?