Hi to install my new smeg plate warmer the instructions say it is necessary to provide a bipolar cut off device in the power supply circuit where the opening of the contacts is more than 3mm. What is this device where can I get one in the UK and approx how much will it cost also the item says it should have a 10A fuse where do I get one of these? Many thanks Phil...

I wonder if they meant "Bi Metalic", like the round disc on water heaters, and used in thermostats, or these:
Bimetallic Thermostat,Adjustable Bimetallic Thermostat,Bimetal Disc,Bimetal Disc Thermostat,India (http://www.aithermostat.com/bimetallic-thermostat.html)

I am sceptical that it would require something so unusual as this would make installation quite difficult and am now wondering if they meant a RCD dual pole socket

It sounds like a mechanical relay with an opening of more than 3 mm when the contacts are open. I'm thinking that "bipolar" means both legs of the circuit -- line and neutral.

10 amp fuses and holders are available everywhere.

Found this:
Smeg CT15NE2 Built In Black plate warmer (http://www.shopwiki.co.uk/search/Smeg_CT15NE2_Built_In_Black_plate_warmer?loose=t)
I wonder now if it also means a 2 pole breaker. If so, they could have said a 10 Amp bipolar device? Good Luck