There are two types of Mk2 Ignition barrel
The early 75AB – 3675 – A1B body
And the later 77AB – 3675 – AA
First up the early 75AB – 3675 – A1B
To release the spring a hole has to be drilled through the body. To mark this up place the body with the column mount towards you and mark a spot 5mm up from the rim around the body and 5mm in from the vertical cast mark on the alloy. Dot punch to help the drill start and then drill a 4mm hole. Go carefully and stop when you feel it pop though the body so you don’t damage the lock barrel inside.
Now with the key in position 1 so you can pull on it poke a screwdriver into the hole and push the spring behind, gently pull on the key and the barrel should come out.
The later 77AB – 3675 – AA
No need for a drill on this one as the spring is visible through the slot on the side. Again with the key in position 1 push in the spring and pull on the barrel gently.