I can't remember much about it as a kid, but I do remember the toys and its really bugging me.
I watched in in the early 2000's before Doctor Who in 2005 as well as Ace Lightning, so it may have been on CBBC.
I only remember that it was live action, about this teenage boy and girl who where stuck on another world (kind of icy or at least there were icy worlds) and the guy can somehow change his limbs to be mechanical. There was a scene where the girl is being taken by the lead villain and as he reaches out for her, his arm transforms into a spring like arm that springs forwards and saves her to his suprise.
There was also a silver C-3PO-looking robot and a giant bird-like creature (I think) as their allies in a pod like spaceship.
There was once en episode where the pod could only use its legs for some reason and had to walk instead of fly.
The toys were really cool and easily available in the UK, and you could detach all the limbs to mix and match different characters since that's what the characters do in the show. Kind of Like LEGO but proper figures.