At the moment, the wait is 10 working days. There is no way you can speed this up, not even with bribery. I'm sure you can deliver your application to Aviation House personally, but they will not do it for you there and then - you will just remove the postal delay.
The irony is that a PPL will be approved within a day or two of them receiving your application. For some reason the issue of the actual certificate takes the time.
Samson