In 2022, Les announced that the site had come back.
Months later, it quickly disappeared again, only to resurface at http://old.atoptics.co.uk.
That link stopped working in 2025 but Les announced that he had uploaded the site to a new address at https://www.atoptics.org.uk. I had copied the site here for my reference but recommend you access it through Les' new link instead.
Screenshot from 2020: