I think he is trying to do several things. He's avoiding the self-laid trap provided by Corbyn's ineptitude that the right are ready to exploit (for purely domestic electoral reasons...and who can blame him) and he's also moving himself from LOTO to a NATO leader at a time when actual threats to the UK are looming.
Its not pretty, it's very easy to criticise, but national leaders rarely have the luxury of taking the moral high ground with no consequences, and this has to be viewed within the context that Israel will ignore all hostility and therefore grandstanding over it would amount to purely making us feel good about ourselves rather than having any material impact.