Regulation for rewring back box?

planning permission is not needed for electrics unless changing the appearance of a listed building, so unless this is a historic castle, forget that.

Very few things are notifiable under building control part P. and replacing an existing back box with a bigger one, or a replacement of a cable that gets cut a bit short certainly isn't. 

New circuits and wiring in bathrooms are the triggers, come back for more info  if that applies. 

But your use of words like ‘code’ worries me - it sounds like you may be reading American texts, and their wiring methods are different, as is their approach to inspection and testing. Do not try and use 110V land methods here.

You could do worse than look in the catalogue of a well known supplier -example  https://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/index.html at the sort of wall boxes available,  and see what fits the switches you have in mind.

You do have to be competent of course, regardless of works being non-notifiable. 

IF you are unfamiliar with UK practice, then you could do worse than to read https://www.flameport.com/electric/lighting_circuits/index.cs4  JWs excellent guides to know what to expect.

And then come back here if it makes no sense.

Standard UK wall box dimensions are  reproduced here

https://www.canford.co.uk/TechZone/Article/BS1363-BS4662-Dimensions

Mike.

planning permission is not needed for electrics unless changing the appearance of a listed building, so unless this is a historic castle, forget that.

Very few things are notifiable under building control part P. and replacing an existing back box with a bigger one, or a replacement of a cable that gets cut a bit short certainly isn't. 

New circuits and wiring in bathrooms are the triggers, come back for more info  if that applies. 

But your use of words like ‘code’ worries me - it sounds like you may be reading American texts, and their wiring methods are different, as is their approach to inspection and testing. Do not try and use 110V land methods here.

You could do worse than look in the catalogue of a well known supplier -example  https://www.tlc-direct.co.uk/Main_Index/Boxes_and_Enclosures_Index/index.html at the sort of wall boxes available,  and see what fits the switches you have in mind.

You do have to be competent of course, regardless of works being non-notifiable. 

IF you are unfamiliar with UK practice, then you could do worse than to read https://www.flameport.com/electric/lighting_circuits/index.cs4  JWs excellent guides to know what to expect.

And then come back here if it makes no sense.

Standard UK wall box dimensions are  reproduced here

https://www.canford.co.uk/TechZone/Article/BS1363-BS4662-Dimensions

Mike.