@KristianS Tested on Sunday successfully. Unfortunately, when I actually needed it last night, the weather was shocking and so my mobile signal (3) was pretty flaky, resulting in a couple of inverter timeout responses from WW.
The problem we have, which is entirely of my own making, is our home broadband is a 4G modem with EE sim (we're out in the sticks, no fibre, fixed line 2Meg max), for which I buy a 15month pre-loaded sim, except I forgot to order the new one in time, doh!
Should be all fixed by this afternoon.
P.S. If you ever need this kind of thing, check out Sancom (via Amazon), they're top notch.