It depends on the design of the lamp. Some are easier then others. you can get gu10 230V lampholders here http://www.tlc-direct.co.uk/Products/TLGULH.html and led gu10's here http://trade.ledhut.co.uk/ It's about a mornings work.[url]
Get an electrician in to sort it before you electrocute yourself. Swapping wires around by trial and error is not safe. An electrician will have the proper test equipment to trace the correct wires.
were the transformers his idea or yours? you would be better with mains led lamps. they might cost more to buy but you will make that back on the electricity and replacement lamp costs.
the key switch will be to isolate the fan for maintenance. diagram has been copied from another forum. i can't remember the posters name, but i'm sure they wont mind me using it.
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I was just pointing out that if the op had been searching goggle, he might have been confused by the different terminology.
And the sooner we go our own way and leave england behind the better.