Why are UK immigration officers so strict and angry all the time, (a bit of a rant) ?

Because they are humourless drones, who have got the power to make your holiday an absolute nightmare. I remember once I returned to Bristol Airpoirt from Lanzarote and an un-uniformed woman sat in an unmarked booth shreiked at me for ping her without showing my pport, I laid into her alright. I don't know who the hell they think they are to be honest.