[proddick]

I plan to buy all the stuff, route the cable etc and then pay an electrician just to connect it to the consumer unit and sign the work off.

I suggest you find one willing to do that before you buy anything. I suspect it won't be easy as they aren't usually keen - for many reasons!

Personally I think the commando solution looks a mess outside, but each to their own. It will need a correct dual pole RCBO to protect the circuit - attached are notes from Ohme. I wouldn't cut corners - safety is important.

 

[proddick]

The electrician who fitted my zappis was very happy that I wanted to put the cables in myself. It saved me quite a bit and he didn't have the hard work of routing the cables through all the awkward places they had to go to keep them as hidden as possible.
I had said that's what I wanted to do before they quoted and he advised me on the cable I needed to buy etc.

Sure and a lot of people here have dug trenches and put wire in etc, but that is a lot different from buying all the stuff yourself, doing 95% of the work and then saying to an electrician "I just want you to connect this wire and give me a certificate"