Re: If I object to my face being scanned and I pull my jumper up over my face
"What about my right to privacy?"
TL;DR - in public you don't have any privacy.
The general argument is that if you are out in 'public' spaces (ie. walking the streets, in a shopping mall, at the cinema, eating out, etc) then you have not expectation of privacy, as anyone and everyone is able to see you.
While you are quite free to pull your jumper over your head, wear a mask or do other things to obscure your face in doing so you inadvertently bring attention to yourself. AFAIK it is not illegal to obscure your face unless the police tell you to identify yourself (usually that involves comparing some form of photo identification against your actual face), so you may run into issues there. Also were you to obscure your face around anywhere there are valuables (say a bank, jewelry store, etc) then it's likely, again, you would quickly bring attention to yourself. Having said all that I note that some Muslim women get around quite fine with full face veils and can say 'don't discriminate against my religion' if challenged. Not sure how they go around banks, jewelry stores, etc.
There are methods to confuse facial recognition systems using clothing, but I believe these only work on against specific algorithms, so you would have to know what you're up against and dress accordingly (if anything had even been designed to confuse the systems in your local area) and then you'd have to keep on top of any changes that might be made to said algorithm(s).