In message , BraileTrail writes
OK, thanks to everyone for the advice and opinions.
I tried a smallish hammer with several blows and that didn't work, so I might try a larger hammer to finish what I started in the garage.
I am putting some more sockets in the garage soon as well and intend to use plastic trunking screwed to the wall for that. However the equipotential bonding to the gas meter is a long run outside so I think I will try drilling and plugging, trunking or a wooden batten wouldn't look right, the cable itself will be bad enough!
To NT, I also liked the old type of flexible metal clips and all the existing cabling in the garage use them, but I can't find out where to buy them anymore.
Thanks, BraileTrail