Thanks to everyone for their help and suggestions.
In response to napolibill:
Yep outage, we had nothing though the HH was still functioning as a wireless router otherwise just not for my VDSL connection. Very odd!
In response to John_Gray
Absolutely. He has a phone, tablet and laptop none of which apparently allow him to get a connection. That in itself strikes me as very odd. His equipment is certainly modern enough to support WPA2. Do you think he would leave home? That would be ideal I can buy more lizards.
There is a very good chance of interference from neighbouring connections. There are certainly a number of wireless connections in the area.
Reply to jchamier & MHC
That sounds like a very good plan. I will certainly suggest that tomorrow and see what happens.I think we already tried turning off all other devices other than my son's but it's worth another try to check.
The wireless signal strength to the best of my knowledge is fine. Wireless works fine from the room my wife and I share and the bathroom and the landing all of which are adjacent and only separated by thin internal walls. Not that this would rule out a problem in one room of course. I shall try your suggestions and report back what I find.
Very many thanks for all the help.