The same breeder advertised on gum tree:
http://www.gumtree.com/london/89/32808589.html
There is a video of the dogs on there. They all seem to be panting heavily in the video which worries me slightly.
To be honest I would proceed with extreme caution. I wonder why these dogs are being advertised on free ad. sites.
Even if you have previously owned a giant guarding breed it will not prepare you for owning one of these dogs. You have to know the breed to know what you are taking on. Often the males will not tolerate other large male dogs and if one of these dogs gets into a fight believe me you will not stop them from killing the other dog.
That sort of size and strength is impossible for even the strongest man to hold back. Often with these type of dogs no amount of training will help - when they snap they really go, no matter what you do or say.
If you are looking for a dog that you can safely walk down the street on a normal lead and keep as a normal 'pet' dog then I would say forget this breed.
Believe me, I know what I am talking about as I own a similar giant guarding breed, he is VERY independent and headstrong and has been a liability all his life. You can forget holidays etc. as no kennel will hold him (he snapped a heavy duty bolt in two at a kennels where I worked).
Please, unless you know the breed very well proceed with the utmost caution.