My repeated answer to this, arrived at through personal experience of spending repeated 10-12 hour days outside right through the year, is a pair of Portwest overtrousers, with a Buffalo Super 6 jacket and a £20 Peter Storm ‘waterproof’ zip up over that, and a standard Helly Lifa as a base layer.
The cheapo Millets jacket sheds the worst of the wet, the Buffalo just gets slightly damp on the surface, and the wearer stays nice and dry and warm as a result. No turning into a boil-in-the-bag human, and no worrying about a multiple hundred pounds jacket needing fancy treatments to shed the water that a £20 nylon jacket does just as well, without the worry of scuffs, snags, tears, etc, which can be sorted with a few inches of duct tape. As a nod to company safety policy, I’d wear my hiviz vest over the top of everything else.
That was my standard winter wear for five years, ‘cos the issued jacket was crap, by lunchtime I’d be almost as wet inside it as the outside was, with half the day still to go.
The Buffalo is hanging up upstairs, and with the weather being what it is, it won’t be long before I’m wearing it again.