Joke: Traveller: How do I get from A to B?
Local: Well if I were you I wouldn't start from A

The point of the above is that unless there is a good lab somewhere in Kent that you can regularly go to on your travels without expense and extra time then the time and expense involved might make it worthwhile to use a high quality lab elsewhere.

I hope you find what you are looking for but if not then you might want to consider trying Agphotographic in B'ham. It has taken over Metro Labs who have a very good reputation. Prices are very good and Matt, the owner, is a regular here and a great guy to deal with.