My two cents on the matter are that neither the German nor British people wanted war. But also we can reasonably expect everyone to violate international law in some fashion if they think it will get them ahead or if they think it's the only way to hurt the enemy. If the Germans had not initiated terror bombing, the Allies surely would have in the lull after the Battle of France. The same applies vice versa of course, as well. Same goes for things like respecting neutrals' sovereignty. If you believe your country will derive a major advantage from a violation, you will almost always do it. The difference is not so much in the basic willingness to violate law, but in war goals, which in the case of Nazi Germany were inherently criminal, whereas British goals were lawful. If your war goals are criminal against all the laws of man, it follows that you will in pursuit of them not respect the laws of civilization.The British establishment of the time, including the most powerful members of the cabinet, and the Prime Minister was extremely, near myopically, focused on avoiding war. In fact, the thing they can, and have, been criticized most for is being so committed to avoiding war that they ignored provocation and failed to prepare the nation for the war they should have seen coming. An accusation most often defended against by the equally true rejoinder that the British people were broadly hostile to any act that might lead to increased tensions and the possibility of another Great War.
In other words, niceness had nothing to do with it. In the considered opinion of a majority of the British public and the leaders of the British political establishment, it was very much not in Britains interest to go to war. Which makes the 1930’s and 40’s about the epitome of “don’t start none, won’t be none”.