They would have to intercept my application for a postal ballot (signed in the little box by me) and the actual ballot paper also signed by me.
But, Marmardoit, what if someone collected them from people who didn't intend to vote and asked for /obtained their signatures, then set about some quiet forgery? Or coerced people into voting the way they told them to?
Or someone quietly extracted some of the returned votes that were for the 'wrong side'? It appears that some counts aren't as scrupulously conducted as they should be. I seem to recall the BBC politics correspondent in 2019 announcing loads of votes for tories before she should have been able to...
Not being the incredibly suspicious type (no, I really, truly, in general, am not,) I actually think that even postal voting fraud is probably negligible. But I think it's likely to be easier...