I would like to add my experience related to leather care of my Bayswater in oak natural leather.
I bought a bag some years ago and treated it the way Mulberry suggested (spraying it with Collonil waterstop spray was the only suggested treatment) - I did it several times and saw the leather "opening up" on the top and these white, opened pores were very visible. I posted the photos on forum as well and contacted Mulberry, as the bag was only several months old.
From the Customer Service, I got their usual response (advice to spray the bag and that my "opened pores" on Bayswater were related to usual wear and tear. For anyone understanding anything about leather, it was clear that something was happening with leather, but I was scared to treat it with any nourishing cream.
I put the bag on the shelf and have not used it ever since, by this spring.
Then, with usage, the white pores started showing up more and more.
As desperate as I was, I decided to use Collonil Gold Premium Leather Polish I had for treatment of my other bags.
As a conclusion - it worked WONDERFULLY, all whitish spots have turned into the oak colour and there are no more dryish zones and the polish has not affected the bag colour!!!

(Although at least 5 SAs involved in selling Mulberry (in various shops throughout Europe) advised me against the polish).
It might have been posted somewhere already, but I anyhow decided to post it - the story which should have never happened if someone had advised me what actually to do.
One more experience - I treat the handles with For Handles Only cream by
http://www.lovinmybags.com/ and have not seen any darkening so far, although it is to say that I have not used the bag much, so it is to be seen in the future...
I hope this has helped to someone...