Don't know what his recipe is, but from what I could see on The Great British Bake Off it looked like it had WAY too much water in the dough. Focaccia does need a wetter dough than normal, but not as wet as it was depicted. You'll never be able to work it like that.
I've based my focaccia recipe on the one I saw in Dough. 300g flour, 200ml warm water, teaspoon salt, teaspoon yeast, 2 tablespoon olive oil. Mix all that lot together and knead as normal. Instead of shaping into a loaf, put it onto an oiled baking tray, pour olive oil all over it and press your fingers right into the bottom of it so you get a flat bread full of finger holes. Cover with cling film and leave to rise. repeat the finger thing, cover with clingflim and let it rise again. Repeat, making sure each time it's got lots of oil on it. Bake it quickly because it's thin, and sprinkle it with crunchy grains of salt just before you put it in.