Thanks, everyone, for your interest and help.
It seems a shame that Origo's, which seem very popular have gone out of production.
Yes, Arne and David, the HPV does look like a possible alternative. And, perhaps, it could be replumbed to a separate fuel tank.
I lived on a boat with a spirit stove with an integral tank at one time. It worked well - apart from a propensity to catch fire if I wasn't careful enough in filling it. The spilt meths would catch fire, the flame would be invisible and it would heat the tank resulting in boiling meths shooting out of the breather hole. Quick action with an extinguisher needed! I can vouch for the fact that meths fires are easily extinguished.
I have messaged Nick and Andy. Thanks.
Matthew