It’s an offence to refuse to provide your details. It’s compulsory, not optional. I’ve had someone come to my front door and demand I fill in the form.
there is no law requiring you to register in the UK
You’re talking bollocks.
“What happens if you do not register
You must register to vote if you’re asked to do so and you meet the conditions for registering, for example you’re 16 or over and you’re British or a national of an EU or Commonwealth country.
If you’re asked to register and do not, you could be fined.”
Exactly (i.imgur.com)
Register to vote for the General Election (www.gov.uk)
I assume most people here already are registered but just in case: here’s the link.