Peter tries his hand at open-water swimming with help from Keri-Anne Payne Carmen Valino

THE first Great London Swim at the Royal Victoria Dock this Saturday will feature wetsuited members of the public ­writhing their way through the mile-long course.

Like the event’s inspiration, the Great North Run, the swim is open to people of all abilities. The biggest draw, however, is world champ and Olympic silver ­medallist Keri-Anne Payne.

The British swimmer will join the thrashing mass, having barely towelled herself dry after winning gold in the 10km open-water race in Rome last month.

If, like Payne, you’ve entered or are just thinking about taking up swimming as a fitness hobby, she has some invaluable advice.

“It’s the best exercise you can do because it uses all muscle groups in your body and is low impact,” she says. “But poor technique could do you harm, especially in the long term. If your stroke isn’t right you could end up with a sore shoulder.”

But, Payne says, the most pressing need for good technique is to improve efficiency through the water.

“The idea is to streamline your body, so there is little ­resistance in the water.”

And I can believe it. Payne put me through my paces at the Serpentine Lido in Hyde Park. Watching her is like watching a sleek torpedo, barely disturbing the water.

I, however, have all the grace of a sea lion – a beached, immobile sea lion slapping its fins on the rocks.

Lengths of an Olympic-sized swimming pool Payne can do in an hour: 60. Me: six, before dying. Hours in a day that Payne trains in the water: four. Me: zero. The first thing Payne notices about my “technique” is my inability to breathe out underwater.

I’ve never been comfortable in open water, ever since having a panic ­attack halfway between the shore and the buoy my teenage pals and I dared ourselves to swim to. Thus, my body doesn’t trust ­itself to exhale underwater.

“By keeping your head above water, your hips sink lower, increasing your resistance,” Payne says.

She advises taking in small breaths of air every two or three strokes, then blowing out through my nose underwater. It’s tricky, often ending in a splurting mess of bubbles and desperate gasps for air. But after a few goes, a rhythm begins to develop.

I’m also in the mindset that kicking my feet furiously will get me to the other side quicker. Not so, says Payne. Again, by splashing my feet through the water surface, my resistance is increased. Subtle flicking of the feet underwater is what’s needed.

However, my front crawl stroke was “pretty good” apart from the bent wrists (keep them straight with ­fingers together). But the breaststroke needed some work. Paddle the water with your hands, while your elbows shouldn’t go beyond your back. Also, when you kick your legs out, your feet should be at a right angle to your shin, acting as an oar. After these minor (ahem) tweaks, my stroke improves to the point where I’m powering through the water twice as hard as I was.

Just watching an Olympic swimmer in full flow is eye-opening enough. But if you’re competing on Saturday, ­concentrate on your own swim or your star-struck head will get a knock from a stray limb in the melee.

To enter the Great London Swim, register at greatswim.org

There are still a few hundred places available, £35 entrant fee