> You consent to this by agreeing to drive.

I'm also NAL, but the idea that you consent to any test by agreeing to drive sounds dubious.

> refusal to provide a sample is the same as intoxicated driving. I believe the UK is such a jurisdiction.

for refusing a sample you are likely to be arrested (under suspicion of DUI) if you "do not have a 'reasonable excuse'" not to be tested. You can give a reasonable excuse, such as a medical one, which would probably play into the courts later.

I don't know further details because there seems to be confusing terminology around what is directly illegal, versus indirectly illegal - e.g. seems things can be "an offence" but also have stated "defences" to them, such as a reasonable excuse, which seems to imply "a defence in court".