Indeed, a prevalent issue, as mentioned earlier. If you want to access the adjuster wheel and set it to free, you can remove a grommet from the backplate of some of them. As far as I can recall, the Fiesta Mk7 does not have this feature, and I would assume that earlier models did not either.
Turn off the handbrake adjuster and check that the cable isn't getting tangled up when you press down on the lever. Then, as mentioned earlier, hit the drum with a large, soft-faced hammer—or, if you're okay with that, a regular hammer—but preferably a heavy one. Turning on the wheel might get you there, but it's highly unlikely. At the very least, you can attempt driving in reverse and forwards to see if you can reach it while the wheel is on.
Hopefully, you can remove the drum if that doesn't work. If your handbrake becomes stuck, you can unfasten it by removing one or two small torx screws; otherwise, you'll have to prop a bar under the studs to prevent the drum from turning! If they're corroded, you can drill off the heads. After that, you can try to remove the drum by screwing a suitable bolt into the threaded hole that Ford should have provided. If you can, spray penetrating fluid into the space between the drum and the backplate lip, and give the sides a more liberal whack; this will also aid the process.
A friend of mine once drove the short distance to the garage while the rear wheel was locked and dragged behind him—not a good idea!