They were not the occupiers when they left Europe, but they certainly were when they drove the legitimate owners off the lands that they had farmed for centuries, and they still are when they forcibly occupy and evict people from their homes today, over 60 years later.
The Palestinian mandate was a
legal commission for the administration of Palestine, the draft of which was formally confirmed by the Council of the
League of Nations on 24 July 1922 and which came into effect on 26 September 1923. They were there only to fill the power and administrative vacuum after the removal of the Turks. At no time did they ever claim to annex Palestine.
There is absolutely no comparison between the British Mandated Administration of Palestine and Israel's 60 year record of disenfranchisement murder and continued theft of land.
So now they were not occupiers, but in an earlier post they were? Yes, prior the existence of the UN they could not be viewed as refugees. This thread is a bit strange, when it change between today and the time period prior WWII