...sometimes I'd be seated in front of the TV with my notepad, trying desparately to jot down what the announcer was saying! Sometimes it worked, often it didn't and so the next time I'd try again.
It doesn't seem to be a good method. I used to practice it with my French, and the more relaxed I was, the better it worked. The best results I was getting was when I tried to concentrate on something else than on understanding the meaning of what they are saying. For example, I was trying to pay attention to the gender of nouns or to noting the occurences of the preposition "à" in the phrases uttered. It directed my attention away from grasping the sense, so the sense came quicker and more easily. It's like when you try to fall asleep: the stronger you want to immerse into sleep, the less likely you are going to have it coming to you - you must simply start thinking about something else.
it would be great if BBC4 started showing a subtitled Polish series like they do with Italian & French series
I think that TVP Polonia does this sort of thing.
A good method could be following a Polish series without subtitles that present good, distinctive contexts and a lot of conversation (which serieses usually do). One of these is "Świat według Kiepskich" on TV Polsat whose all characters except Ferdynand (Ferdek) Kiepski and Arnold Boczek use proper Polish. The wife of Ferdek, Halina, speaks typical standard Polish, while their neighbour, Marian Paździoch, shows the tendency to abuse the newspapers language with expressions typical for the print rather than for the every-day language, but that makes him really funny and isn't that bad for the learner of Polish.