Thanks Colin. With your help I have resolved the problem. Cheers.HI there Pinky and welcome to the forum
First question would be, is the windowscreen heater also staying on as well as the on light?
That would not be good. Faults could be the switch contacts jambed on, if so replacement of switch required, or more likely the windscreen heater relay for the circuit is jambed on, again replacement relay required.
Temporary you can disconnect the circuit by the fuse for it. Check the fuse number in the fuse box (see car manual for fuse number), and then start from there and check these two components out.