I was under the mistaken impression you could refuse and then would get a blood test, seems that was wrong/out-dated (also wrong!). The backup test at the station is also usually a breath test apparently. And it seems we have field sobriety tests but it looks like they're for drug-driving.

For example, https://www.gov.uk/stopped-by-police-while-driving-your-righ....

I took OpenAI's references as correct without checking legislation as I'm on my phone.