Gaps between socket and back box

[ml1936]

Is there a reg which states its wrong for socket boxes to sit too far back behind plasterboard?
When galv boxes where fitted, walls where just getting patched back in, now some bright spark has dot and dabbed the wall with further plasterboard meaning socket boxes are good 10-20mm too far back!
I know longer screws can be used but is there reg about there being a gap between socket cover and back box, allowing dust etc in?

 

[comms]

You could possibly use 527.1.1

 

[ml1936]

So is it best to bring boxes forward, or if plaster is completely between box leaving no gap is that ok?

 

[comms]

In the real world leave as is.