Only the results of a blood test are admissible in court (not speaking from experience).
the roadside test is an indication. Some devices give pass/fail, some give a numerical result.
As sbob says, the station procedure is evidential breath, with blood or urine as “statutory options” if there is a medical reason they cant provide the breath, or the result is within a certain range of the limit.
There are to many variables to apply general rules, if I have 1 pint in the day I am on my arse but I can drink wine in the evening and feel no effect. I dont drive after either.