From page 4 of the Big Red Book.
"Existing installations that have been installed in accordance with earlier editions of the Regs. may not comply with this edition (17th) in every respect.
This does not necessarily mean that they are unsafe for continued use or require upgrading. "
"Existing installations that have been installed in accordance with earlier editions of the Regs. may not comply with this edition (17th) in every respect.
This does not necessarily mean that they are unsafe for continued use or require upgrading. "