I once read a wonderful monologue on how countries that are friends manage to stay friends by spying on each other. After all, the more you know about each other, the less distrust. I don't doubt the UK's secret service have file upon file of information regarding foreign diplomats.
Right or Wrong is a more complex issue, firstly, Wikileaks are mostly publishing the opinions of Ambassadors who are performing a very difficult dance, any Ambassador who is thought to be 'going native' often finds themselves re-assigned to another post, they aren't there to like the country involved, merely to represent the interests of their own country. Secondly, even the acts which are morally questionable do not automatically make themselves required reading for the general public, that can often increase tension and beligerence and make a solution less likely, rather than more, sometimes a little behind-the-scenes work can do far more good than shouting it from the rooftops.
As Mongoose stated, it's not really a question of the morality of what has been said or done, it's about Wikileaks decision to release that data to all and sundry.