Sky are good, and their network is one of the best. TalkTalk Business are also good from what I have been told. I am with Zen and I cannot fault them, although they are pricier than most others. It might also be worth considering Uno. They have packages running through BT Wholesale and TalkTalk Business, however they provide the customer service, and from my experience it is incredibly good. They respond to tickets at all times of day, I have had responses at times ranging from 8PM, to 3AM, to 6:30AM.
At the end of the day it is up to you and your brother to decide, but my recommendation would be either Zen or Uno. Both are solid options, with Zen having their own backhaul in some exchanges while Uno relying on TalkTalk Business if you get their slightly more expensive packages.