Ha, fixed it!!
Didnt realise that one of the switches was only active during the period when economy 7 was active, so had no power at this time of day!
Well i am a student and today i learnt something new!
Ive just ripped out the storage heaters in my mums flat to fit in some new creda electric heaters for her.
When i removed the storage heaters, there were 2 cables going to 2 switches. One was a fused switch and one was a standard single switch.
Now ive fitted the creda heater and ive wired it...