ericgibbs is correct that this example of isolation transformer from RS is not suitable. This example is a low power signal transformer for audio isolation. You need a power transformer specified for use on 50Hz mains. The most important specification will be how many Watts (or VA) it is designed to pass, and in your case the number of watts (or VA) must be equal to or greater than the number of watts of your lamps.
The smarter solution is to alter your circuit to isolate the input and output, since an isolation transformer is large, heavy, and expensive while an optoisolator included in the design is small, cheap and efficient. But it has to be done carefully and correctly.