Many thanks for the reply guys. Just a few more points about the Mtb.
Would the battery be fitted where the water bottle carrier is and would it need any more fixing holes
Would the fact that the bike is carbon and light have any issues with these kits
The bike owner has it advertised for £400 would that be reasonable and worth converting.
Speed is not a major factor for me more range , some hills but nothing too serious would 11.6 battery have a decent range if not needing much assistance
Sorry, I forgot that it's carbon. That really makes it complicated.
Forget about a down-tube battery. Instead, you should use a battery in a triangle bag.
You need to study your rear drop-outs to see where the metal starts and ends, and how well it's attached to the carbon. If you're not careful, it could twist the drop-outs out of the carbon tubes. For a rear motor, I think you'd need to fabricate some special torque arms that can spread the load along the frame or take it all the way to the BB.
A middle motor might be possible, but it depends what type of BB you have and how thick the carbon is around it.
My advice would be to keep that bike as it is and buy a used one with an aluminium frame to convert t electric. £200 should get you one that's pretty good. There's not really any advantage of a carbon frame when you have electric assistance.