Gordon H wrote:
snippy
There is only one safe way to do it. Get a qualified electrician
to lay a preferably armoured cable, that's what I did for an 8ft run
to my garage. It doesn't need to be 3ft deep, but I covered the
cable with small hardcore, then a couple of inches of concrete which
a spade or fork will not penetrate!
snippy

May I suggest you run the armoured cable through something like inch & a
half waste pipe, so cable can be withdrawn if needed,
--
Pete C
London UK