Well i finally had chance to fix the rear brake (and do a service), i have to say what a pain in the arse.
The job it self was not too hard, just one of those jobs! I couldn't release the brake pipe from the caliper because it had welded it self, i thinking 7 years of dirt + a lot of heat. So i had to remove the metal brake pipe with the caliper.
Managed to get the piston out it was quite dirty and rusty. Pug wouldn't sell me the piston, only the whole caliper £120 ish and they didn't have one in stock. Visited 3 scrap yards hardly a 406 to be seen and not one with rear disks. In the fourth one manage to find a already removed caliper (on the ground under a V6 estate!) with recently damaged seals, the piston looked better than mine but not perfect, had to buy for £10.
Then had to split that caliper, clean the piston and rebuilt mine. All done and the brake is not longer rubbing

, just hoping the "new" piston is good enough and i don't have the same problem again!