A blue overhead sign suspended over the motorway from a post on the left, with a downward-pointing arrow indicating the left-hand lane, and the following text.
A10 ; London (N & C); Enfield; Hertford.
Junction number: 25.
This junction is a standard two-bridge roundabout interchange, but the A10 is much too busy for that to be the right answer any more. Its location right next to the mouth of a tunnel, and hemmed in on all sides by encroaching suburbia, means that it's unlikely it will ever be upgraded in any significant way.