That's Polyplumb/Polypipe, but Hepworth Hep2O is grey as well.
Unscrew the collar and pull back out of the way.
Twist the grab ring of with a pair of pliers (spikey metal ring)
Use a new grab ring or a new fitting to replace.
not quite sure the builder. As I'm at work I trying to think. They didnt have a collar you can unscrew. The pipes seemed to be pushed into the inlet fixing on the shower.
When I get home tonight I'll take a photo of it and put the photobucket link on this thread.
Ok. I'll keep an eye open for the photo.
It may be that the shower has its own "female" fitting built-in. i.e. you simply push your pipe into it.
Whichever it is, if there's no un-screwable collar, then you may have to hold the collar firmly and push it away from you (towards the shower unit), then pull the pipe out.
Most need the collar pushed into the fitting and then pull the pipe out. If you've already tried to pull the pipe out without pushing in the collar you may find it now quite a job to pull it out but persevere, it will pull out.