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It's a well-known fact that St Paul's was the loftiest structure in London until Battersea Power Station's chimneys sprung up. But a forgotten pair of towers got there earlier... and were even taller.
The twin towers in question were a pair of electricity pylons like the one shown above. They carried cables across the Thames between Horseshoe Corner, Dagenham, and the Crossness/Thamesmead border.
At 148 metres (487 feet), the towers were among the tallest structures of their kind, anywhere in the world. When completed in 1933, their tops were over 36 metres (120 feet) higher than the tip of St Paul's. This was a couple of years before Battersea Power Station became the first structure in London-proper to outgrow the cathedral, at 113 metres.
The twin towers supported cables carrying 22,000 volts from Barking Power Station across the river for distribution through Kent, Surrey and Sussex. Work started in late 1931 and was completed by March 1933. It was visible for 15 miles around. Press at the time called the structures "A great British triumph", and "An electrical parallel to the Forth Bridge".
The towers needed to be so high to allow plenty of clearance for shipping. At their lowest "droop", the cables were a clear 76 metres (250 feet) above high water, meaning that even the largest vessels could still pass beneath. Between them, the behemoths supported 42 tons of electrical cable.
The towers were painted with red and white stripes, to aid visibility during daylight. They were capped with red neon lights to help aircraft at night — now a commonplace, but then quite a novelty.
So, were either of the pylons London's tallest structure? No... but oh, so very nearly. Dagenham and Crossness were, at the time, areas of Essex and Kent. However, the Kentish tower was just a few metres from the Metropolitan Borough of Woolwich, which was in the County of London. Had it taken a step to the left, then the tower could legitimately have been called the tallest structure in London.
As it was, the Crystal Palace transmitter bagged that title in 1950, reaching 219 metres into the south London sky. The Thames pylons would eventually become part of the capital during the creation of Greater London in 1965 but, by then, they'd also been overtaken by the Post Office Tower (now the BT Tower).
The towers were eventually dismantled in 1987. Even so, the Thames does still boast the tallest electricity pylons in the UK. A few miles downriver (in proper Kent/Essex) stand the 190 metre towers of the 400 kV Thames Crossing, between West Thurrock and Swanscombe. They're taller than the Gherkin, and an imposing sight, towering over the river and marshland. All power to them.
Photographs of the original Dagenham/Crossness crossing are very hard to find online. Here's a low-res one from the Illustrated London News, or you can see the original if you have a sub to the British Newspaper Archive.
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