Not too expensive if you don't need waterproof RCD units -

http://www.ebay.co.uk/itm/63-amp-2P-...-/300887701552

http://www.ebay.co.uk/itm/63-amp-3-p...-/261197634015

Definitely worth checking what overall current draw your household would have if you went out & fired up the plasma and the compressor kicked in whilst someone indoors put the kettle on and had a quick shower whilst the immersion heater warmed up the water for a proper soak ;-)

- Nick