Mine took precisely 3 weeks and 1 day-
I delivered the paperwork in person to Gatwick and had it checked in situ on 11th March. The Visa payment went out on the 18th, and with nothing seen by the 31st I rang them up.
After wating an absolute AGE on the phone, I spoke to a very helpful person who assured me that it would be sent out recorded delivery that night, and I got it on 2nd April.
So maybe ringing up does help
So I can fly to Duxford this weekend with my first passenger!
Cheers
SD