Now, four wired ports were never going to be sufficient for my needs as I had things then, so I have the two portables both operating over wireless networking and the wired connection from the one in "Mission Control" (as I call this room) has been removed.
The other one, located in the bedroom, I had already set to wireless networking, so no change was needed.
However, the other bedroom computer (ha ha! Take that, Modesty Blaise!) – a RiscPC – had previously communicated with my eight-port LinkSys router via a pair of Belkin wireless devices, one plugged into the RiscPC and the other into the router.
The router will not work with the Virgin hub (at least not with the limited tinkering I have done so far) so my new idea is to wire the bedroom RiscPC into the portable's network port and use that machine (in RISC OS emulation mode) as a "bridge" between the wired and wireless networks. It will be interesting to see (a) if this works at all and (b) if the bedroom RiscPC is visible only on the connected portable or is transmitted across the whole network. I suspect it might be the latter, but haven't yet reached the point where I can test it.
It's because that RiscPC has only a 10Base2 (BNC connector) network interface. I have a gadget to convert the signal to 10BaseT (RJ-45/UTP) which I have wired up, but I can't find the mains power unit for it. There is relatively little still boxed up here, but I have spent a whole afternoon untangling various cables from one packing box and it wasn't among those.
Okay, so I shall carry on looking during the next couple of days, and no doubt report back what transpires. As I backup these "secondary" computers only monthly, on the first day of each month, it would be handy to have this working by some time tomorrow (1 April)!
UPDATE: I've found the power supply for the gadget, and the bedroom RiscPC and the hard-wired portable can now see each other; but that is all. Not a problem: I shall simply 'pipe' anything to or from the RiscPC via the bedroom portable, which is no trouble at all. Indeed, this gives that machine more work to do, which is no bad thing.