By and large, Diascia are perennial, just not necessarily in the UK. I've never managed to keep one going longer than a year, but then the soil's quite heavy here - they tend to prefer well drained full sun situations. Suttons are advertising one that's supposed to be properly perennial, but whether it is or not I can't say, see here
http://www.suttons.co.uk/Gardening/Perennial+Plants/All+Perennial+Plants/Diascia+Plant+-+Sundiascia+Rose+Pink_233851.htm

Than you Bamboo.

I kept one going for 3 years then lost it in the winter 2011. not done them since though they are nice plants.

They are lovely plants but I've found they don't survive in a really cold winter. Having said that I still have one that's thriving after flowering all last summer.