https://www.liquidgasuk.org/uploads/DOC65F1825C7F50A.pdf has the Code of Practice from 2017 (whether that is when the distances were revised I know not).
Which says, about existing installations, where they met the regulations in force at the time...
a) the installation met the relevant requirements of the Standards and Guidance
in force at the time of its installation and the installation does not present a
safety risk; or
b) a risk assessment demonstrates that the installation does not pose a significant
safety risk.
