Yay! I am so happy you started this thread because they are my agency and I love them and I was feeling left out of the whole "do you know this agency" thing in this section.
They are fantastic and represent some of the top authors in the UK and the world. Lee Child is one of their clients, as is Martina Cole and John Connolly. All of these authors are internationally bestselling. Aside from that Darley himself is wonderful to work with, really nurtures talent, helps authors grow.
Julia left, yes. It made me most sad because she was my agent and fabulous and actually became a good friend. But Darley took me on when she left, assured me that I would not be left on my own, and has more than lived up to his promise. He is still looking for her replacement, but as far as I know they are still accepting submissions for children's literature.
Personally they have sold my book to over 10 countries, and got me excellent deals in all of them. They are there to help mediate any issues I might have with my publishers, and answer any questions I might have. I thank my lucky stars that they wanted to work with me.
You should know that they are particularly fond of commercial fiction though. They like plot driven, fast paced, marketable work. They do represent a wide range of authors, as you can clearly see from their website, but mysteries and thrillers are definitely up there on their favourites list.
Anyway, in conclusion, they are a fantastic agency, considered one of the top in the UK, wonderful to work with and definitely worth submitting to. Definitely.