Hegemon88 you started your own thread on this literally a few days ago so I'm not sure why you've posted again here, here's the reply that I took my time to write considering I'm based right on the edge of the Stansted zone and have transitted quite regularly in the last couple of years:
According to my logbook I've transited Stansted a total of 8 times in the last 2 years and Luton twice - I've not been denied once (yet!).
With Luton you have the prescribed lane, both times I stuck to this and it was very simple - they normally just ask you to report at each VRP and to hold short of crossing the active runway until they give you the go ahead.
With Stansted it's much more unpredictable. The key thing is they don't really like letting you in if it's a bit pointless, if you're just cutting a corner for example. However, if you need to actually get across the zone either width-ways or length-ways, they'll accommodate you if they can but do expect long periods of orbiting. I think it's useful for the controllers if you can give them a a position according to one of their VRP's so that they know exactly where you plan to enter/exit. Once I was told to hold for approx 15 mins near Audley End VRP before they finally let me in, another time I was in almost straight away but then had to orbit short of the runway for about 10 mins. Once they sent me 'over the active threshold no higher than 1500ft' and made me change to the tower controller whilst overhead (which was great!), another time they routed me over the top of Bishop's Stortford, and then through the ILS track several miles away from the runway whilst keeping me on the radar frequency only.
The key thing I always stick to which seems to work is:
Initial Call: "Essex radar, this is G-ABCD, request zone transit"
Essex Radar: " Standby"
Wait anything between 30 seconds and 5 minutes.
Essex Radar: "G-ABCD, squawk 1234"
Me: "Squawk 1234, G-ABCD"
Essex Radar: "G-ABCD, identified 2 miles north of Audley End, pass your message"
Me: "G-ABCD, 2 miles north of Audley End, 1500ft QNH 1013, from Cambridge to North Weald, request zone transit Audley End to Great Dunmow via your overhead"
Then wait and follow instructions!