Attached from BS 7671:2018.
"The regulations apply to the design, erection and verification of electrical installation, also additions and alterations to existing installations".
Adding RCBOs is an addition and/or alteration to an existing installation the way I understand this so it would need to comply with BS7671:2018 rather than the original standard at the time of the installation 20 years ago when my MCU was installed. I guess that why these electricans won't touch RCBOs in plastic units and advising new consumer units but I could be wrong.
"The regulations apply to the design, erection and verification of electrical installation, also additions and alterations to existing installations".
Adding RCBOs is an addition and/or alteration to an existing installation the way I understand this so it would need to comply with BS7671:2018 rather than the original standard at the time of the installation 20 years ago when my MCU was installed. I guess that why these electricans won't touch RCBOs in plastic units and advising new consumer units but I could be wrong.