Hi
Yesterday I found this spider, it's around 15mm and was found sitting on the head of my horsefield tortoise. 
I was amazed at this little spider, it is the first UK arachnid I've seen being defensive and giving a threat posture.
It was been given a temporary home in one of my small tarantula enclosures and has now been returned to my garden.
Am I correct with the I.D?  I would like to learn more about these.