I wonder why these things are called energy savers, they take ages to get anywhere close to warm, and because of that they use the same amount of electric as a higher powered heater but take longer

better idea safety wise, but not a power/energy saver, at least kettles heat up quick

60 watt seems pretty low for a heater, which is 0 .006Kw. 600 watt is 0 .6Kw which is not much, but more realistic and should pull approximately 3 amps from your supply. 1.5mm cable is rated for use at 5amps so the cable is sufficient up to 5 amps. However 1.5mm cable is not used for power circuits, generally only lighting circuits. Power circuits sre 2.5mm which is rated for use to 13 amps. You can spur off 2.5mm power circuits then fuse down to 5 amp protection and then use 1.5mm cable to your heater. Probably the cable entry into the heater will be round heat resistant cable which will need to be properly terminated in a socket box with a double pole isolator switch. All in all I would be employing an electrician if I were you. Electricity is not to meddled with and can be lethal if incorrectly installed. Also when you come to sell your house you may need to prove the heater was correctly installed by a qualified person.

Cheers Concrete

I think you mean 60 watts is .06 Kw, not .006. As you say 1.5mm cable is for lighting, which suggests the heater is only 60w. Probably advertised as low energy but without comment on effectiveness.