When walking along the Regent’s Canal are you aware that you’re walking just inches above a major electricity cable supplying London with power?

You can see where the electricity cables run, by the series of concrete paving slabs, some conventional width and others quite narrow that run along the canal towpath. And the many warning signs, aimed mainly at canal boat users who might otherwise drive a spike into the ground to moor their boats.

Installed in 1976-9, initially between St John’s Wood and City Road, these are two powerful 400 kV power cables. Over the years, the network has been extended, and now runs from Harlesden (at the old Acton Lane power station) along the Grand Union Canal to Paddington, where it joins the Regent’s Canal and loops around London.

It runs past Victoria Park, and joins the Lee Navigation before diverting back up towards Stratford, and terminating at Lea Bridge.

The reason for their location under the canal towpaths is both practical and interesting.

Firstly, if you want to lay a lot of power cables across London in the late 1970s, there was a very convenient semi-derelict route — the run down canals. At the time they weren’t the picturesque delights that we see today, but a shabby relic of 1970s industrial decline.

So, the body that managed the canals was rather welcome to the idea of earning some money from leasing out the towpaths to an electricity company. Although not everyone approved.

But the convenience of avoiding the need to dig up tons of roads was not the only reason for choosing the canal.

Cables carrying that much electricity get warm. Very warm in fact. So warm that deep level power cable tunnels have to have ventilation shafts to provide cool air.

But, here there’s another ample supply of coolant — the Regent’s Canal itself. Pumped canal water is circulated as a coolant for the high-voltage cables.

The water isn’t in direct contact with the electricity cables — for obvious reasons.

The cables run through concrete trenches, which also contain water pipes. The electricity cables warm up the air in the trenches, and the water pipes cool it.

The installation of the electricity cables had an unexpected side effect, as by the time they were installed, the canals were a bit run down from the collapse of their industrial use, and their use for leisure hadn’t taken off.

In order to lay the concrete toughs along the canal for the cables to sit in, the electricity board had to clear away a lot of overgrowing plants which were blocking some of the towpaths. In doing so, they inadvertently opened up the towpaths to pedestrians, who have used them ever since.

In addition to clearing the canals of overgrowth, when the CEGB was seeking permission for its cooling and pumping stations, one was planned to go near Camden, next to a boys club. The council insisted on something “interesting”, so that’s why there’s now a Pirate Castle on the Regent’s Canal.

In fact, there are eight pumping stations along the canal, although the rest are more anonymous.

Over the decades, the power cables running under the canal towpaths have continued to supply electricity to London, although upgrades have taken place.

Not just to the electricity cables, but on occasion to add mooring rings, after a potentially fatal accident when a mooring pin was hammered through the side of the protective concrete trough.

In 2006, the National Grid, which now manages the old CEGB infrastructure had to install new steel sheeting along part of the canal to protect it from the risk of oil leaks. Although the cable troughs are water cooled, oil is also used for insulation and cooling, and a leak was considered a serious risk.

In 2010, they refurbished the cable cooling system for these cables. The refurbishment also included work on two header tank buildings, three valve houses, seven outlets and a cable tunnel.

Since the power cables were laid, other utilities have taken advantage of the easy conduit around London, and there can be found a number of telecoms, and in some places, gas supplies running under your feet.

When they were dug by the Victorians, the canals carried energy in the form of coal to be burnt in homes around London. Today they are still carrying energy to London’s homes, in the form of electricity, made from coal burnt miles away.

A final quirk of the power cables though – remember that they use water from the canal as a coolant? The heat from the cables is still warm enough through the concrete covers that on very cold mornings, that heat can melt most of the snow and ice that would otherwise build up on the canal towpath.

The Regent’s Canal comes with underfloor heating!

In fact, the Canal & River Trust get the occasional email in the winter months praising their apparent diligence in keeping the towpaths clear of ice, not realising that it’s a useful side-effect of a 40 year old decision to lay power cables along the Regent’s Canal.