In all my time based in Essex and flying around Stansted and requesting zone transits, I have only ever received one and that was when I landed there back in 1990! It's Class D, so should be available on a tactical basis. Maybe filed in the 'too difficult' box?
So now, I never bother speaking to them. IMHO, the most unhelpful ATC unit in the UK
Actually, that's not quite true. Shoreham & Redhill are equally unhelpful