Front Gates - how wide at minimum should it be?

We are about to build a front wall and buy a set of gates but I think they might be a bit narrow. We need to get diggers and dump trucks in at some point for groundworks/landscaping - just worried they wont be able to get in.

So what width at a minimum should front gates be?

If you wish to make a new, or wider entrance, planning permission will be required. Is that a factor here?