I have a Ford Focus 1.8 Diesel Estate 51 reg i.e. Sept 2001.

The battery light came on, but the alternator is still charging but the heated windscreen button light does not come on when I press it, if I turn the ignition off and back on the fault clears, can anyone tell me what the problem may be, its happened twice over a period of the last 4 days, I drive approx 130 miles per day as a taxidriver and I have had ford focus's for about 8 years now and never had this problem before.

Regards John

I'd get your battery health checked.
I'd suspect the heated screen not coming on is due to the car detecting an unmanageable power drain and protecting itself.