Its a Regal Pelargonium. There are hundreds of named varieties so couldn't say which. Unlike their zonal relatives, they have a distinct break in their flowering from mid summer until late spring the following year so yours may soon finish.

Thanks for the ID and info.

They need a cold period (around 10º C) to stimulate the formation of flower buds.

Well, that shouldn't be a problem here in the UK currently - plenty of nights recently where its been below that temperature (she says sarcastically..)

lol....True! I would have expected there to be more problems with them freezing this year, even though they are more frost tolerant than the Zonals (P. hortorum). I should have been more specific, though--they need average temperatures of around 10º, not just at night.