The other half has come back tonight reporting that even when set to cd the heaters are blowing red hot. Then it will go fold then hot any ideas. It's a 55 plate ka collection is it the radiator coolant level appears ok. No temp gauge in the car.

Almost certainly the Heater Control Valve. They are prone to fail and they either Stick in the hot or cold position. Your best bet is to get one from Ebay, the cost is only about £15 (they are a generic ford part for all MK1 KA's and transit vans etc so there's no need to find one specific to the StreetKa)Changing it is pretty easy takes about 30 mins. look up on google ford ka heater control valve of try the links below m8

look here

or here

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDkQtwIwAA&url=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DnFaf4dCz--c&ei=3zejUKzDEuPR0QWlpYDABg&usg=AFQjCNHWRn00IfYXA2zOKljFu3EkjD7_Ww&cad=rja

I recommend getting one directly from Fords. Normally under £40. Some of the eBay ones only seem to last 6 months before failing again.