Hi there. I'm instaling a 3m UHF for a customer, and I've always powered all previous UFH from an RCD breaker (sparky doing the connection fom me). In this job the customer doesn't want the fuss of running a new wire from the consumer unit under the stairs to 1st floor bath, lifting floorboards etc.
Is it possible, and above all is it legal, to power UHF from a socket using possibly a fuse box and fused thermostat? Any ideas welcome as my sparky is on holiday and cannot be contacted.

It can be connected off the ring via an spur but not directly to a 13amp socket via a plug. How old is the consumer unit? Are the breakers up to date, RCD protected?

thanks Scottley, thats good news then. Consumer unit is updated, less than 10 year old with full RCD protection

If its RCD protected then it should be ok, but of course you will need to check that with your sparks, but is certainly deosnt have to go back to the board on its own circuit/radial.

Depends on how big the installation is. Things to consider are:

1. Total wattage of circuit - i.e. if wattage per sq m is 200 - you install 20 sq m in conservatory, thats a 4KW fixed load. What else is on that circuit? Will it overload it? Many ufh installations are in kitchen - you could end up with dishwasher and washing machine on same circuit - both have 3kw water heaters inside them. (yours is 3sq m not a problem on ring circuit).
2. You must wire the installation through a fused spur, fuse appropriate to heating load. (Probably a 3A fuse in your case).
3. Cables must be installed in a safe zone (directly vertical or horizontal to accessory) not within 50mm of gas or water pipe (although they can cross, just not run alongside).
4. Only most recent electrical installations have a properly managed consumer unit with dual RCD breakers - system may require upgrading. You must be fully qualified to sort that out.
5. Installation should include a plan of cable layout in floor (your responsibility) and a notice attached to consumer unit (this installation includes under floor heating....etc).

In all honesty, the customer should be referred to an electrician, unless you got C & G 2381 qualification....

Or unless you get it signed off by building control.

Thanks andy8758, I appreciate your reply, very informative.