BOAC,
If you are on an ADSL link, then what you describe sounds like the MTU setting is incorrect which can be the case with some ISPs.
The old grey matter isn't quite what it used to be & I no longer use ADSL so can't check my own settings. If you are on ADSL then I suggest you look at
http://www.kitz.co.uk/adsl/MTU.htm. For some reason I have a recollect of setting the MTU to 1600 and that some routers couldn't go this far.
Hope this points you in a direction that helps