Regardless of any arrangements the Brits had made with the Jews back in England, they actually had no legal or moral right to allow Jews into Palestine as it was not their country to give away, they had already recognised the Palestinians as the legitimate owners and agreed that it was to become their homeland in 1915.
Yes,... the Brits could have legally allowed the European Jews into their own country, as could many other countries which did not. So, as far as the "guilt trip" is concerned they were no better or worse than any other country that turned back the Jews.
In view of the fact that Jewish terrorism was already a huge problem within Palestine it can be strongly argued that the Brits did actually have an obligation to prevent further trouble by preventing illegal immigration to Palestine.
The British never made any agreement with the Palestinians that they would get a country. The only agreement Britain had with Arabs was that they would support Arab independance if the Arabs sided with the allies during WW1. This is why Palestine was severed in 1921 and Transjordan was created. Palestine is never mentioned in the agreement with the Arabs.
The only agreement that mentions Palestine is the Balfour declaration promising Jews a homeland here. The Balfour Declaration became binding international law when the League of Nations adopted it as part of their mandate in Palestine.
While it is correct that the country did not belong to Britain, it didn't exactly belong to anyone else either. Britain inherited it from the Ottomon Empire, which became defunct after the first world war. The only independant political entity to exist in Palestine were the ancient Jewish kingdoms. There has been a continued and unending Jewish presence in this land for more than 3,000 years and we never renounced our claims to a country here. The only reason Israel is 63 years old and not 3,000+ years old is that we were conquered several times. Even when we did not have independance here, the country was ruled by foreign empires that never eatablished another nation here.
The fact is that the British had the most ability to do something to help the Jews and didn't as a matter of policy makes them worse than countries who were not in a position to do as much. Some, like Denmark and Bulgaria, did way more to help the Jews than the British Empire.
"In view of the fact that Jewish terrorism was already a huge problem within Palestine it can be strongly argued that the Brits did actually have an obligation to prevent further trouble by preventing illegal immigration to Palestine."
The Jewish underground groups made retalitory attacks on Arab militants after being attacked themselves and were formed as a response to Arab massacres against Jews in the 1920s and 1930s. It was during these massacres that the British refused to defend Jews or allow the Jews to defend themselves. It was a result of Arab uprisings that the British issued their "white papers" and limited Jewish immigration.
It wasn't until they backtracked on their commitment to a Jewish state in order to appease the Arab mobs that fringe Jewish groups began targeting British military outposts in order to get them to leave.
The pre-state Jewish underground didn't use attacks on civilians as a matter of policy. They targeted Arab militants and British soldiers. The few cases in which civilians were the result of an organization called LEHI. Most of these casses involved assassinations of British officials and were widely condemned by the majority of the Jewish community.
They are not to be compared with Hamas, which targets only civilians and are supported by most Palestinians.
Also, the British created the Jewish "terrorist" problem when they backtracked on previous agreements and then refused to defend us from Arab attacks while simultaneously allowing the Arabs to arm themselves.