Later this month, a bale of straw is to be hung from the Millennium Footbridge as a warning to boats on the Thames.

It’s an ancient bylaw of uncertain heritage that if a bridge arch is open to river traffic, but has the headroom restricted, then a bale of straw should be hung from the bridge as a warning.

And, as it happens, later this month, contractors working on behalf of the City of London will be conducting surveys on the Millennium Footbridge, and the head room of the bridge will be reduced by up to 2 metres.

The works take place on the 21st and 22nd April 2015, so look out for the oldest of bylaws enacted on central London’s newest river crossing.

But only during the daytime. At night the bale of straw is replaced with a light. Sadly, an electric one, not a burning bale of straw.