Inform the electrician (Qualified ?), that you are bring in an indepent expert in and he will be charged for the cost as well as the cost of repair to your equipment.
The oven shoud NOT run from the fuse box (13amp), but from it's own box (30 amp)to be legal.
I have never heard of an electricial running live cable outside the house, unless it is 'Armoured cable', (which I doubt).
I hope you have not paid him/her yet.