Lucian Truscott, the Texan general whose troops liberated Sicily during the Second World War, would have little sympathy for British postmen who are complaining that they are being asked to walk at 4mph.

But the inventor of the Truscott Trot, which stipulated that soldiers under his command should march at 4mph, never had to deliver 180kg of letters and parcels single-handedly to residents of a South London suburb.

The Times dispatched its longest-legged reporter yesterday to determine how fast Royal Mail’s postmen really are. The answer seems, on paper, to be unimpressive.

The postman, who asked to remain anonymous for fear of a reprimand from his manager, spent 3 hours covering a route he said was 1.5 miles, giving him an average speed of less than 0.5mph, but the figures are misleading. The length of the streets may be 1.5 miles, but tramping up serpentine garden paths means that the distance is doubled or tripled.

The Times’s postman is not blessed with an athletic physique, but he is deceptively quick. His average speed is so low because he is rarely travelling at a steady pace. He must slow down for every garden gate and pause at almost every house to push letters through inconveniently small letterboxes.

Parcels take even longer. Residents are rarely poised by the door and most are out, requiring our postman to fill in a short form to notify them that he has visited.

The rise of online shopping means that the number of parcels in his trolley has swelled to 20 times what it was five years ago, and the workload increases exponentially at Christmas.

There are also hazards. He knows exactly where the six dogs on his route reside. “When you’re a postman you know where all the dogs are. There are about five on my round that are really vicious. I’ve got one who headbutts the door every time I post something through it. He just charges at it.”

There is a scrabbling noise outside a door marked with a “beware of the dog” sign. “Listen to the mad dog here. It’s a massive old boxer.

There is more danger in slippery paths, he says. “I fell over the other day. I was wearing the Royal Mail regulation shoes, so they can’t complain about that. I think the earth moved.” He holds his arms up to mimic a dog lying on its back. “I was like a dog.”

There are perks to speed him on his way. Grateful customers tip their postman, although it has been thin pickings so far — a single box of chocolates. There is also the prospect of residents appearing in various stages of undress. “It is a big surprise how most people are dressed when answer the door. There was one woman who came to the door wearing just a towel wrapped around her, and it did fall off. Put is like this: she was a very nice woman. If I weren’t a married man...”

Royal Mail claims that it does not ask its postmen to travel at 4mph, but a presentation created by the company leaked by the Commercial Workers Union suggests otherwise. It contains instructions on how managers should use Pegasus, a program that calculates how many houses a postman can serve. The presentation states that walk speed should be set at 6.44kph (4mph).

A spokesman for the company declined to comment on the leak. “Royal Mail carefully plans every postman and postwoman’s walk so that no-one is asked to cover a greater distance or deliver more mail than they are capable of doing and it is complete nonsense and completely untrue to suggest otherwise,” he said. “The speed at which we ask our postmen and women to walk is around two miles per hour and the systems we use to help us plan the most effective delivery walks are used in many other countries and have been successfully used nationwide in the UK since 1996.”

The Times’s postman has not been instructed to walk at a given speed, but said that routes in his area were reduced by a third earlier this year. The result is that he and his colleagues must cover more distance in the same time. “We can’t do it any faster, so it will just take longer.”

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