Although, I think it is harsh - it is the law.
Only reason why I say it is harsh, is that it's down to luck; For example we are both same height weight etc etc and both go out to drink and drink the same high number of drinks, we depart from our drinking pit, you get caught immediately - reading is 100mg = HRO. I drive home 'safely' nap but then decide to go out to get some food 5 or so hrs later, this time I get caught but blow 45.
The only thing here that distinguishes myself from you is that I was lucky in all sense; not to get caught, not to cause injury/damage, not to be classified as HRO - whilst at the time of driving home from the pub I'd have been HRO. It's a difficult law to manage
But I still hold that simply because it's an arrestable offence doesn't make it right to punish every first offender with a lifetime criminal record.