Just been on the website
Lighting-Direct and at the top of the screen it states the following:
PLEASE NOTE THAT PROBLEMS HAVE ARISEN DIMMING HI SPOT GU10 LAMPS
WE ADVISE THAT ONLY IQ OR REMOTE CONTROL DIMMERS CAN BE USED AND THAT THE TOTAL WATTAGE USED MUST BE NO MORE THAN HALF THE RATING OF THE DIMMER SWITCH