[Madhatter]

Just been down and enquired, a hedge is not a boundary, it's a boundary treatment. it's not a aboundary fence that can't be over 1 metre, it's a fence next to a highway, so the end of a dividing fence could be covered by this, say the bottom of two back gardens both end with a road going across them, the bottom fence and the last two metres of dividing fence can't be over a metre high.

On the plus side, it's four years here so may be dour there. If it's been up four years and that sounds likely you don't need permision. You'd have to prove it with witnesses and preferably photographs, but Maybe witnesses will be enough.
The planning department will have had to have recieved a complaint to do this so don't think they are against you. I'd confirm the time in yrs first 4 5 or 7, then check with neighbours see if you can get anyone to write to say it was there, height and roughly how long in years it's been there. also contact the people who put up the new fence, they will confirm that there was an old fence.