The scaffolding surrounding the Charing Cross railway bridge has received an addition – two bales of hay/straw – because an ancient law requires it.

The law requires a bale of straw to be hung from a bridge as a warning to mariners whenever the height between the river and the bridge’s arches is reduced, as it is at Charing Cross at the moment.

According to the Port of London Thames Byelaws, Clause 36.2, a bale of straw has to be placed under London bridges “when the headroom of an arch or span of a bridge is reduced from its usual limits”.

At night, the bale of straw is harder to see, so some warning lights are also switched on.

Quite why a bale of straw is needed has long since been lost to time, but regardless of its origins, whenever the river bylaws are updated, they kept the medieval bale of hay law intact.

At the moment, what is officially the Hungerford Bridge into Charing Cross station is undergoing the first phase of several years worth of maintenance work, which will see one arch at a time covered in scaffolding to allow the work to be carried out.

As the scaffolding hangs below the bridge – it triggers the old law about restricted heights under a bridge, so the contractors needed to buy a couple of bales of hay.

For convenience, they’re actually hanging from the Jubilee footbridges, one on either side of the railway.

At the moment, one railway arch has the bales of hay as the height is restricted, although the arch is still open to river traffic. Over the next few years, the scaffolding will move northwards along the bridge, and the bale of hay will need to move along with it.

So, for the next few years, there will be a bale of hay hanging from the Charing Cross railway bridge, because an ancient law says so.