This sounds like a real beginner's question, but I'm really struggling with changing the pads on my 2009 Fiesta.

As per the guide in the Haynes manual, I've removed the wheel, removed the brake hose clip, undid the two bolts securing the caliper to the mount, and tried to slide off the caliper itself... and it's here where I become unstuck.

The caliper's definitely loose, and I can start to slide it off easily by one or two centimetres, but it then gets stuck on something. I'm pretty sure it's not the pads, as they're already quite loose, it's as if there's something metal stopping the caliper from sliding completely off.... there's a definite 'stop'.

Any ideas?

Probably just the lip on the brake disc where its slightly worn. take the cap off the brake fluid reservoir, wrap a rag round it in case off overspill and get a screwdriver between the back pad and the brake disc and gently lever it back to give you a bit more clearance between the pads and the disc, then try again.

There might be a clip securing the caliper in place I read somewhere how to do it but cant quite remember

Look at the piccy of the pads make sure the clips have been removed, Im assuming you had removed the clips when I replied.

http://www.ebay.co.uk/itm/Genuine-Ford-Fiesta-Mk7-2008-Onwards-Front-Brake-Pads-/320803704795?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Model%3AFiesta&hash=item4ab1640fdb

dont think those clips are what Dangers was referring to, as those clips cant be removed till pads are out.

think he means the clip on the front face of the caliper as you look at it from the wheel side.

they are fairly easy to remove, can be a bit awkward to refit if not used to them...good tip would be take a pic before you remove to ensure you refit correctly.

if that clip has already been removed, then could just be what was suggested earlier...push piston back slightly to give a bit more free movement

could also be the pad is sticking to the carrier top and bottom, just need a bit of persuasion to help free off, usually a gentle wiggle between pad and disc at the sticking point/s will work

Many thanks for all the suggestions. 'charlie866' was close to the answer, but the problem wasn't the lip of the disc... it was two notches sticking out of the pads themselves stopping the ring of the piston sliding off (see attachment).

Once I managed to push the piston in further with a screwdriver, the caliper eventually slid over them.

Thankfully the replacement pads didn't have those notches, so if and when I need to change them agani the process should be a bit more straightforward :)