A21

From the M25 to the bustling towns of west Kent, the A21 expressway will get you on the way to Hastings.

Kent is rather remarkably well served by major roads leading to and from London. There's the A2 and M2, of course, and the M20. Further east, the A299 extends the major roads to Thanet. And then, in the western corner of the county, there's the A21. But Kent doesn't like sharing its major roads with anyone else - the M20 doesn't go to France, you see, it just stops when it's reached the coast. And so the fast expressway of the A21 rushes through Kent but comes to a halt and reverts to the old single carriageway A21 before the route crosses into East Sussex.

This 15-mile expressway was never conceived as a continuous high-speed route - at least not when its first parts were built. It's actually a series of three bypasses, linked in 2017 with a couple of miles of new road, that flow into each other. Together they bypass and serve three of Kent's major towns - Sevenoaks, Tonbridge and Tunbridge Wells.

The A21 is unusual in having more expressway built than is actually available to drive. In the mid-1960s, construction on the Sevenoaks Bypass was seriously delayed when a section running along a hillside just north of the village of Sevenoaks Weald was found to be unstable. Five major mudslides were discovered, carrying material to an underground lake, thanks to a massive geological fault that had not previously been known about. As a result, the new road was steadily sliding away.

The bypass to the north of that point was opened with a temporary tie-in to an unclassified road called Gracious Lane, which served as the main road until the stricken section could be rebuilt. In the end Hubbards Hill bridge and a section of new road more than a mile in length had to be demolished and rebuilt on a new line 250 metres to the south of the original. Rebuilding a road on this scale is virtually unheard-of in the UK and the problems encountered on the A21 Sevenoaks Bypass are among the worst ever encountered so late in the construction process. Aerial photos to this day still show the line of the original dual carriageway through fields to the north of the modern road.

Since the Sevenoaks Bypass was opened, there have been aspirations to extend the route to reach the coast at Hastings, on and off, for years. But no significant progress has ever been made, for two reasons. One is that the existing road is never quite busy enough or problematic enough to rise to the top of the to-do list. The other is that right now there is nothing much to terminate a high speed expressway on once it reaches the outskirts of Hastings.

The proposed Bexhill and Hastings Bypass, a major trunk road scheme of the 1990s, would have provided somewhere to end an A21 expressway, but that was cancelled a long time ago amid much environmental concern, and has not been seen since. In the meantime, the odd new bypass does appear. The most significant is at Lamberhurst, which looks as though it hopes to one day be part of a London to Hastings expressway, but for now it's just a couple of miles of isolated dual carriageway between two roundabouts.

For now, though - and indeed, for the forseeable future - the A21's motorway-like section reaches from the M25 out to Pembury, 15 miles of exceedingly fast and effective dual carriageway with fine views of the Weald to enjoy on the way. And if you're going to Hastings, enjoy them while you can, because the journey slows down considerably when it ends.