It looks the mechanism that returns the push button on the door handle is rusted beyond repair. Initially i couldn't open the door, I have now managed to be able to open it but it won't close unless i push the piece inside manually (The piece to the right of the orange plastic in the attached pic)

Bustersbus has done a great step by step guide here how to do it all (I borrowed a section of his pic to attach here....hope he doesn't mind?).
My problem is the screws holding the handle on seem to be rusted....I can't get enough torque on them to undo them without rounding the head. I've a feeling it will be a drill the head off...
If I undo the 4 bolts holding the window mechanism on will this be a pain in the arse to put back together.....I am an expert at taking things apart but putting them back together is always a major challenge!

Does this help?

Thanks Marmaduke, its getting to the bits thats the issue at the moment

No it's not too bad taking off and putting on the bit that holds the window winder. I took mine off last summer and it wasn't hard to get back together at all. The most difficult bit is the spring clip that holds the window winder handle on.