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THERE’S a very bizarre reason why an iconic landmark that appears in Harry Potter has to have bales of hay hanging from it while it’s repaired.

The straw dangles from the Millennium Bridge in central London during the day to warn ships passing underneath that the headroom is lower than usual.

Under the Port of London's by-laws a bale of hay must be hung from a bridge during the day while it is being repaired
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Under the Port of London's by-laws a bale of hay must be hung from a bridge during the day while it is being repairedCredit: Twitter/@CityBridgeFndn
At night, the hay is replaced with a white light
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At night, the hay is replaced with a white lightCredit: Twitter/@CityBridgeFndn
The pedestrian bridge featured in Harry Potter and the Half-Blood Prince
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The pedestrian bridge featured in Harry Potter and the Half-Blood PrinceCredit: AFP

While at night, the straw has to be replaced by a white light.

The Millennium Bridge, which connects St Paul’s Cathedral and the Tate Modern, is currently being repaired for the separation layer between the structure and the deck.

The membrane layer has begun to wear away.

The famous bridge appeared in Harry Potter and the Half-Blood Prince.

Read More on Harry Potter

In the Port of London’s Thames rulebook, by-law 36.2 states: "When the headroom of an arch or span of a bridge is reduced from its usual limits but that arch or span is not closed to navigation, the person in control of the bridge must suspend from the centre of that arch or span by day a bundle of straw large enough to be conspicuous and by night a white light.”

It's not known when the by-law was introduced.

A spokesperson for the City Bridge Foundation, which maintains the bridge along with four others, said: “This is one of those quirky traditions London is famous for, but it also does serve a practical purpose, to warn shipping when the headroom under a bridge span is reduced.

“The bundle of straw is lowered by our contractor when they’re doing work under the bridge, in this case to install netting ahead of work to replace the separation layer between the aluminium bridge deck and the steel structure underneath.

“As a 900-year-old charity which maintains five Thames crossings and is London’s biggest independent charity funder, we’re proud of the part we’ve played in the history of London and our modern day role looking after some of the capital’s key transport infrastructure."

The footbridge has been shut for maintenance since October 14 and is due to reopen on November 5.

It first opened in 2000, but was soon forced to close again for two years due to it wobbling.

An investigation was launched and it was revealed that the problem couldn’t be fixed entirely but the wobbling could be reduced with special hydraulic devices.

The bridge is due to reopen on November 5
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The bridge is due to reopen on November 5Credit: Alamy
The foot bridge connects St Pau;'s Cathedral to the Tate Modern
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The foot bridge connects St Pau;'s Cathedral to the Tate ModernCredit: Alamy
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