Hold on, you nor i know anything about what Starmer would have done, he wasn't privy to the real time scientific advice but went along with the 1st LD and there was cross party support (more or less)
We don't know what he would have done later on, remember the job of the opposition is to oppose, quite often, when in power they change tack as they get the real picture.
Not sure why you think it wasn't a safe way of working, by late April 2021, vaccine roll out was going well, most vulnerable people had got a jab and Covid had not proved to be so deadly to younger folk... Starmer could only work to the rules as laid out by the Govt or should he have ad hoc 'd his own ones?