Yeah, there are cranks who say stupid things, but it's common knowledge at this point that the Corbyn campaign was undone by various levels of sabotage by fellow Labour members and even people within the campaign who went to extensive lengths to misappropriate campaign funds to undermine Corbyn while using baroque levels of targeted advertising against Corbyn and his advisers and even the journalists they follow to cover the tracks of those misappropriations. There were surely Jewish individuals and Jewish organizations involved, and Israel itself was probably involved since Britain is an important ally to it, but Corbyn was mainly undone by white British Zionist opposition.

Part of the issue is that western governments -- the US famously has this issue with AIPAC -- seem to wish to bait antisemitism by allowing Israel to use publicly-visible levers of power usually reserved for domestic corporations and "special interest groups" to control politicians. People see the success of AIPAC and they say "Look! Israel controls so much of US politics that concerns it!" They do not stop for a moment and wonder which other foreign countries are allowed to have a PAC in the US that can so freely buy off politicians. Israel has a lot of money thanks to the endless money funneled to it, but they certainly aren't the richest country in the world. In absolute terms, the richest country is the PRC (due to size, population, etc), and yet we see no American-Chinese Public Affairs Committee PAC, this of course being due to the fact that it is not permitted to have one. Israel is allowed to have one because it is chiefly a western puppet, and so it is quite safe to allow it to use these levers of power to ultimately give money back to its masters to secure their own common interests!