Monkeh, gotta agree with Ban-All-Sheds on this one. It's not regulated spectrum, so it's rather unfair that others should have to suffer simply because you believe that your use of the spectrum is more important than theirs. If you want guaranteed bandwidth, move onto a licensed band and buy new equipment. Sorry!
I agree.
Just because Monkeh thinks his use is more important than the others doesn't give him the right to BREAK THE LAW by deliberately cranking up his power to deliberately interfere with them. The fact that he wants to watch high bitrate video doesn't give him any right to ignore the regulations just because he thinks it's more important than whatever someone else is doing.
If he thinks their kit is not compliant he should make a complaint. In spite of my earlier comments regarding OfCom, they can't use the same excuse as they did with BT and PLT since this kit is designed to transmit.
As pointed out, if he cannot make do with the unlicenced bands available, he should go to a different band. It CAN be done with a Mac Mini - it has an ethernet port, so you can plug a client bridge unit into that and the Mac doesn't know it's using radio.
An obvious starting point is 802.11a, or dual band 802.11n. He will most likely find the unlicensed 5.8G band fairly quiet at the moment.
After that, there are various option in licensed bands - but no, I don't know anything about them.
But of course, there are some interesting cabled options too - including a flat cable that could be fitted under carpet as long as it's not in a heavily trafficed area. It's really, really rare to find somewhere that CAN'T be wired - usually it's only DON'T WANT. If it's don't want, then your choice - how much do you want video ?
As an aside, it comes up on the MythTV mailing list from time to time, and the standard response is DON'T. Wireless just doesn't cut it for jitter sensitive streams like video. Some users have had success with PLT (ie use the mains wiring).