This is determined by city by-laws so restrictions can change from city to city. On top of that, it seems like those city by-laws seem to change on a regular basis. So it’s important to check out your city website for the current restrictions and loopholes. Historically one of those loopholes has been that a paving stone walkway running along a driveway doesn’t count toward the width restrictions. With that being said it’s usually a safe bet if you stay within the limits of what your neighbours are doing and simply don’t go overboard.
The following can be found on the City of London On website as of April 2017: