right guys i finally managed to get the f**ker off, turns out it DOES unscrew, but as i was doin it i had to hold the base with a second set of pliers, and the plastic bit of it came off the thread so i then had to unscrew that seperately, needed some WD40 on it though.......
reception on my new aerial is fine, not had any problems tonight, its a Richbrook anti theft one....