@ LLisabeth
As I've heard, British wouldn't have stayed long and they complained a lot about company rules. Moreover, most of the time, there were less than 10 candidates attending an open day.
Therefore, they might have decided to slow down recruiting in UK.
However, it doesn't mean that they ban British people. British are welcomed, and there are still some British joining the company, but they got selected from other places outside UK.
If you really want to join Qatar Airways, at this moment you need to apply from other countries.