World War I poison gas factory added to list of England’s most at-risk heritage buildings

The factory was used to produce nearly 390,000 mustard gas shells towards the end of the war

The National Filling Factory is an ammunition plant urgently built in World War One when it became apparent Britain was worryingly short of artillery shells (PA)

Drivers barrelling down the M40 motorway may be forgiven for failing to notice little special about the line of trees that briefly appears beside the carriageway just south of Banbury.

It is only on closer inspection that the large embankments and concrete footings hidden by the shrubs give up their secret - next to one of the nation’s busiest roads lies a chilling memorial to Britain’s industrial-scale use of poison gas.

The remains of National Filling Factory (NFF) Number Nine, an ammunition plant urgently built in World War One after it became apparent Britain was worryingly short of artillery shells, have lain largely unremarked for a century after the facility which churned out some four million projectiles was dismantled in the aftermath of the conflict.

Naze Tower in Essex, a lookout post in the Napoleonic Wars (PA)

Now the site has been added to the list of England’s at-risk heritage after the passage of time and the growth of trees and shrubs threatened to destroy the physical remains of a stark reminder that 100 years ago Britain was an enthusiastic user of weapons of mass destruction.

The factory, which was built in just three months in 1916 under an emergency scheme overseen by then munitions minister Lloyd George, was used to produce nearly 390,000 mustard gas shells towards the end of the war. The chemical, named after its distinctive smell akin to mustard or horseradish, is a blister agent causing horrific burns.

Historic England has added the remains of the munitions plant to its annual Heritage at Risk Register, which is published on 20 October along with a warning that while record numbers of imperilled buildings and sites have been saved, those that remain are ever more difficult and expensive to repair.

Among the other buildings add to the latest list is a disused Victorian pub in south London which became famous as venue for punk bands in the 70s and a concrete Catholic church in Birmingham by the modernist architect Richard Gilbert Scott, where leaks through the roof are causing it to decay.

Historic England, previously English Heritage, said the Northamptonshire munitions plant was particularly important as evidence of a little-recognised aspect the First World War and its impact on the landscape.

Britain’s oldest surviving roller coaster at Dreamland in Kent (PA)

Thousands of workers - many of them the women - were drafted into hurriedly-built factories to bolster Britain’s supplies of artillery shells after it had become clear in the early months of the conflict that Allied stocks were massively below those of Germany.

The job of staff in NFF Number Nine was to take empty shell casings delivered to the factory and fill them with a hot liquid explosive after painting them inside and out to ensure the volatile chemicals did not react with the metal and detonate.

To minimise the risk of a devastating chain of explosions production took place in a series of separate “filling houses” or wooden sheds, each surrounded by a thick revetment or embankment to funnel blast upwards in the event of an accident.

By the end of the war, the Banbury site was one of the biggest in the country, employing some 1,500 people and filling thousands of projectiles a day. Shells produced in its mustard gas facility were used towards the end of the war to breach the Hindenburg Line, resulting in a report from the frontline that workers should feel “great satisfaction” at the success of their weapons.

Many of the women employed in the factories found their skin had been dyed yellow by the chemicals used in the manufacturing process, earning them the nickname “canary girls”.

The factory was eventually demolished in 1924, in parts razed to the ground to burn off any toxic residues from the explosives and chemicals. What remained was the network of earthworks and short tunnels used to transport the shells around the site and it is these physical reminders of the industrialised nature of the war that conservationists say are now endangered.

Ben Robinson, of English Heritage, said: “There are very, very few sites left which can convey a sense of the process that went on in these factories. But the archaeology is becoming more hidden and difficult to read. If we believe that places such as this are important, then we have to think about ways of keeping them visible and legible.

The concrete Church of St Thomas More in Birmingham is another at-risk site (PA)

“We forget that the First World War also had an effect on the British landscape but they are more and more difficult to find.”

The conservation body said it had beaten its target of removing a quarter of all at-risk properties from the register over the last five years. By 2018, it aims to see a further 750 sites removed the register, which currently lists 5,534 buildings and places.

But it warned the register now features more properties requiring difficult repairs. For the first time the deficit between the cost of repair and the end value of a site has exceeded £500,000.

Buildings newly-added to the Heritage At Risk Register:

* Naze Tower, Essex

Built in 1720, this Napoleonic-era lookout post was used through to First and Second World Wars, including a stint as a radar station. A botched 1970s repair to the stonework using sand and cement has led to severe damp and there is significant structural cracking.

* National Filling Factory Number Nine, Northamptonshire

The remains of this First World War munitions factory lie beside the M40. Originally built to fill shells with high explosive ahead of transportation to France, it was later converted to also produce poison gas. Earth embankments and concrete tunnels are being eroded.

* Church of St Thomas More, Birmingham

Built by architect Richard Gilbert Scott, the 1968 Roman Catholic Church was fashioned entirely from concrete with spectacular stained glass windows. Its roof is leaking, causing some of concrete to break up and flake.

* The White Lion, Wandsworth, London

This sprawling Victorian pub, built in 1887, was a popular live music venue in the late 1970s and 1980s. It regularly hosted punk bands, including X Ray Spex. It now lies empty.

* The Mausoleum of Joseph Hudson, Kensal Green, London

The Portland stone tomb is one of the most ornate in the vast Kensal Green cemetery. Hudson fought in a decisive naval battle of the Napoleonic War before making his money as a tobacconist on Oxford Street. The tomb has become damaged by plants and saplings.

* Old Pier Lighthouse, Sunderland

Built on Sunderland’s old South Pier in 1856, the iron and steel lighthouse was moved to a nearby park in 1983. Water is causing some parts of the structure to corrode.

* Westgate Hill Cemetery, Newcastle upon Tyne

One of the earliest garden cemeteries in England, the graveyard has fallen into neglect with invasive plants and vandalism damaging the surviving monuments.

And some that have been saved….

* Cardington Airship Sheds, Bedfordshire

Shed Number One is the only hangar pre-dating 1918 left in Europe and has been preserved after years of investment and conservation. It measures 50m high and has a volume of 20,000 square metres.

* Scenic Railway, Dreamland, Margate, Kent

Britain’s oldest surviving roller coaster was badly damaged by fire in 2008. It is now one of the star attractions at the newly-opened amusement arcade.

* Brown Bear Pit, Dudley Zoo, West Midlands

Designed by architect Berthold Lubetkin and his Tecton firm, the Bear Pit is one 27 innovative structures in the zoo built using reinforced concrete and is being conserved.