I'm ex police and this is pretty much just a scare tactic.
Firstly, it's not routine to breathalyse everyone at any accident. That's even if police attended.
Secondly you can refuse a breath test (wouldn't recommend it, you would probably get arrested but you can't be physically forced to take one)
Thirdly - how would anyone be able to prove that the amount of alcohol in your system, which is under the legal limit, was what impaired your judgement and control? That's impossible to establish retrospectively.
Fourth, and most importantly - If you were in a serious enough accident to incur a 'penalty' it wouldn't be the police in charge of awarding or deciding said penalty anyway - if you were, for example, charged with careless driving/death by dangerous driving or anything else, then it would go to court, and the judge/magistrate (if you were convicted) to decide on any penalty. The arresting officer judging you for having had a drink is of no relevance whatsoever.
Sentencing has to be in line with guidance - judges can't just randomly make stuff up.
Technically it could result in a more severe penalty but only in so far as pretty much anything - driving barefoot or after not having slept for 24 hours or after taking allergy medication could result in a more severe penalty - it might not be recommended but it's not illegal, therefore in order to use it as a contributing or exacerbating factor you'd have to prove it definitely was one. You couldn't just say 'oh he'd had a drink so his judgement and control was probably impaired even though he was within the legal limit.'
You can only punish people for actually breaking the law, not 'coming close' to it.