Hi All,
I carried out the above procedure recently and followed the instructions of an Australian guy [i believe it was.]
Unfortunately, i failed to insert a suitable pin in the long rod [the one with the long spring on it, within the handle, in order to prevent the sear spinning round.
Should this problem befall you, rotate the sear 180 degrees and fix it in place using an allen key, pushed through the top tapped hole used for the grips. The part then that needs fixing in place is the above mentioned long rod with the spring on it. Use a suitable sized allen key [Not a staple, as i did] and put it through the hole in the long rod to hold it in place.
When the compression tube is then put in place, the allen key can then safely be removed and the pistol should cock alright. I hope this tip will be of help to anyone experiencing a similar problem.