I was onboard. After we landed at Birmingham, I spoke at some length to the captain.
The problem was caused by a failed seal on the rear internal cargo door. We were climbing through 14,000 feet at the time. Crew initiated a (not very) rapid descent. Oxygen masks not deployed. Diverted to Birmingham. Textbook stuff.
There then followed something of a comedy. FlyBe's reserve aircraft was ready and waiting just two stands away but we had to wait nearly half and hour for a bus to take us the necessary 100m.
Full marks to crew and company (though not Birmingham Airport) for geting us on our way in an efficient manner.