The terminology "emergency isolation" is no longer used and is called an "emergency switch-off", largely to remove ambiguity around the term as isolation suggests electrically safe when it's not necessarily the case.
The plan for GWEP was remote switching and electronic securing, but it all got descoped due to cost so it is largely manually operated switches and lock-off, for which you need to be at least an Authorised Person.
The OLE infrastructure in that area are mostly headspans which means that damage to one road can affect the others; that's why the incident on the Queen's funeral was so impactful, as all 4 roads went down in one incident. This one doesn't appear to be quite as bad with only the Down Main affected.
Regarding re-energisation in a situation like this, firstly you need to fully understand how much has been damaged, then start drafting the isolation paperwork to arrange an isolation around that, then implement the isolation, before you can start turning things back on, to mitigate the risk of inadvertently livening up something that would create a risk of electrocution or further damage or fire or whatever. Again headspans complicate this due to the nature of the insulators being part of the span.
About 9.30pm they were ready to re-energise but the ECR were reluctant to given reports of members of public being on the infrastructure. It was around 11.30pm when the Reliefs were brought back in.