Back in 2016 when the new H&S sentencing guidelines came into play, were we the first to implement the changes or did we follow on from how other countries manage H&S offences. (or are other countires looking to follow ) 

Does anyone have an example of the biggest fine so far given were no injury or accident occurred (based entirely on the potential for harm

Having finally woken up again I have revisited the question-“Does anyone have an example of the biggest fine so far given were no injury or accident occurred (based entirely on the potential for harm”

You can only be prosecuted for an actual breach the law. Usually the HSE would be called to the site if there was an accident, and they would try link it to some failure of a duty under legislation eg inadequate training or not suitable and sufficient risk assessment. HSE guidance makes it clear that they wood not prosecute simply because they felt that the  risk assessment was not good enough or that PPE was not being supplied, without an actual incident occurring. In that case they might issue an enforcement notice and if the corrective actions were not carried out then they might issue a fine. But there was clearly a breach of the law in that case not simply presenting the potential of an accident.

See https://www.hse.gov.uk/pubns/hse41.pdf for HSE policy