Thanks, looks like I'll be going down that route. As has been said, speaking to Technical Support will get me nowhere since the staff involved have no idea about the blocking activities higher management have implemented.
---------- Post added at 21:50 ---------- Previous post was at 21:19 ----------
For anyone who may be interested in the problem, here's a plot taken this morning on my PC.
And here's a plot taken at the same time on my friends PC, 9 miles away, at the other side of swansea.
For those not conversant with Ping Plotter, the red blocks on the bottom bar graph indicate periods of no connection.
Clearly not a problem with my router, (although by-passing it does get rid of the dropouts)
And clearly the tech support statement that "We aren't blocking anything, we're not allowed too" is misfounded.