Having just received a reply from the DoT regarding this posting, please find their their comments as follows:-

Parking vans on the diagonal car parking on Loch Promenade.

I can confirm the Department's Parking Controllers have been enforcing this area and any large van (transit size or larger) is to be given a fixed penalty notice if they are parked in the diagonal parking area.

Vans can be parked in the Parade Street car park.

It would appear from this response that the restrictions/enforcements are being applied to the Diagonal Parking areas on Loch Promenade only and not on any other section of the Promenade.

However, always best to check on the day when you turn up with your van.