Don't throw your toys out of the pram just yet, especially on what seems to be a matter of principle. Simply take the scrip, get the meds, put them in the bin if you do not want to use them. The GP is not watching you take your meds, unless you are in hospital with a nurse administering. This way both of you tick your own boxes, and live happily after. Otherwise it will cause angst and could end up with the practice taking you off their books as has happened to others.
If your diet is successful then your lipids should fall naturally and look like "the statins are working" instead of languishing in landfill (or be a good girl and drop them into the local pharmacy for recycling if your conscience worries you)
You have a legal right to refuse treatment. They have a legal right to apply for a court ruling in their favour if they consider you are in danger of harming yourself, but I doubt if refusing Big Pharma is in that category in this case.
https://www.verywell.com/do-patients-have-the-right-to-refuse-treatment-2614982
And for the opposiion
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/138296/dh_103653__1_.pdf