One cat beating up the other

My parents friends (I am posting this thread for them) have 2 cats, Fraiser and Digby, they used to have one called Mitzy as well but she was put down a few months back. Now Mitzy used to be in charge of the two boys (who are brothers by the way) and since she has been gone, Fraiser keeps beating up poor Digby, who ends up running off and not being seen for hours. Digby never fights back, and just takes all the bullying from Fraiser. Is their anything the owners can do to stop Fraiser chasing off/attacking Digby all the time?

Once again, I recommend Clomicalm. I realize that you're in England so I don't know how readily available this med would be but it works wonders w/aggression and behavioral problems in cats. Some vets will automatically say that it isn't approved for cats, only dogs, but ametryptilene isn't approved for cats either but vets regularly prescribe it anyhow. Sometimes it takes a few weeks to see any change but I was fortunate in that it began working for my cats immediately. My 9 1/2 year old cat Specs (who is also a pee cat and Clomicalm has stopped that nasty behavior as well) bullies my old boy Boo who is 18 but Clomicalm keeps him chilled out (not drugged, just not aggressive) w/out any side effects whatsoever. My RB Peeka used to bully my sweet old Pidge, too, but I didn't know about Clomicalm then or I guarantee you, she would've been on it. Perhaps talk to your vet or have your friends talk to theirs and see what they say. For me it was "problem solved". Hope this helps. :)