This may sound daft, but if OP did it himself or used a none approved contractor, what would happen?
I expect the council would not even notice this having been done, it is not like they inspect each and every road is it?
Likely they wouldn't - but if someone reported you or if you somehow made a monumental balls up and went through a pipe or something (no idea how but hey) then they would string you up by the balls.
Plus it would need to be safe, for example if you did it yourself and someone tripped and broke their leg because one of the slabs was a cm too high, you could also be liable.