In the mean time, the fact that many poor ederly people in the UK cannot afford to heat their homes (often because they only have expensive electric heating) is disgraceful.

I envision a charity. This charity purchases server racks and small supercomputing clusters (with about 50 CPUs each). The racks are equipped with a liquid-cooling cycle and a fridge-style radiator at the back.

The charity installs the racks in the living rooms of needy OAPs, along with gigabit fiber internet connections (though in some cases, such as numerical computations, normal ADSL might suffice). It then acts as a web hosting/ number crunching company and rents out the server space/ CPU cycles to anyone who needs it. Costumers could be anything from bloggers to drug companies who need to compute the latest protein structure.

Each rack would produce about 5000 W worth of free heat 24/7, enough to keep a poorly insulated house cosy warm. Room temperature can be controlled by opening windows. Of course, the pensioners in question would need to agree to receive frequent visits from the charity's sys admins, but most would probably welcome the company.

The beauty of this idea is that the charity may well break even, in other words it doesn't need to rely on donations or taxpayers' money to keep pensioners warm.