Just by way of an update, engineer visit first thing this morning and thankfully he had a replacement Hub 3 router with him! 2nd engineer in the space of 3 weeks to tell me that there is a massive router shorter at the minute at VM, which explains why they can't just send out from customer services. They need to send engineers out to check that everything else has been ruled out as the problem.
The wifi drop outs appear to have stopped from the limited 5 hours use today, but the wifi speeds through the new router max out at approx 60Mbps whereas previous router was approx max 400Mbps. Maybe this will stabilise over time, but I won't hold my breath.
One thing I have learnt over the last 3 weeks. Put your Hub 3 into modem mode and plug a decent router into it. Yes, you shouldn't have to, but it made the world of difference in my house.
Asus RT AC86U in my case - currently on promo at Amazon. I can get above 600Mbps wifi on my phone connected to the Asus 5G signal and over 100Mbps 15 metres away at the bottom of the garden.
Either way, VM please consider this closed.
Thanks