Trim off the dead looking lower parts only. Something tells me that it will look like it had a mullet style trim but it’s been around for ten years so being on the conservative side will most likely ensure it’s continued viability.

RHS says they can have regenerative pruning. There are several linked sections for them with this link Stera.

https://www.rhs.org.uk/plants/89372/erica-arborea-var-alpina/details

regenerative pruning
https://www.rhs.org.uk/plants/types/shrubs/renovation

I meant to add try and strike cuttings from anything you prune off as a 'security' measure if you fancy it.

Thank you both. No grief to mew if it doesn't make it as the surrounding things have now matured round it. I'll give it a go and see what happens. Its not pretty for most of the year anyway - like me its seen better days, but I don't think the same technique would work on people do you?...