Fontana you have just been lucky in your flights.
Every day security are issued with a secret internal list of flights that are excepted security screening in DOH that day. This list varies from day to day. However it seems to be that UK flights appear quite often on the list. There is apparently a positive bias toward UK flights and not, as c2lass incorrectly assumes, against UK flights.
It is a rare exception that any other airport, other than LHR, appears on the list two days in succession.