This is not what our trusted friend and forum medical adviser Doc Holiday said in a previous post when it was mentioned before.
Quote from: Doc Holliday on July 03, 2020, 02:05:42 pmThe laboratory component of the test is accurate .. the problem lies with the home test kit being a finger prick blood sample. To be accurate it requires a full venous blood sample .. which takes us full circle to Scutty's collapsing veins 
I'm actually not disagreeing with him if you read what I said.
I should imagine (but I don't know) that BUPA will take blood directly from your vein.
In my personal case I was bleeding so profusely (having used three lancets) that I suspect what went into the provided vial was pretty well venous, and I had meticulously prepared and cleaned my finger before doing so.
As Doc said, the Lab part of the test is (or should be) reliable.