I'll tell you what; those folks at the CEO office know their stuff. As promised, my new VMNG300 arrived today. The chap who had it mailed to me recommended calling the office directly rather than going the 151 route, so I did that and reached one of his colleagues who absolutely knew his stuff (we were swapping stories about our various tech projects outside of work) and had the MAC registered and going within a few minutes, with the speed boost from 20Mb -> 30Mb following about ten minutes later. No paying £30 here.
What an improvement: ping and jitter have been halved even compared to the reliable Ambit 250, partly because the household is now on the non-legacy network. Plus, my third-party router setup can remain the same rather than with the Super Hub, which never gelled well with any of it. I even offered to send the damn thing back, but the chap wisely recommended I hold onto it for now, just in case.
I sent a name-checking letter of commendation to their line manager, I was so impressed. This is the service everyone should be getting! I'm pretty sure I'll be going up to 50Mb soon, as there's very little uptake of the DOCSIS3 network in my area, which ensures outstanding performance at almost all times.
I'm off to set up a broadband monitor...