Mind the Gap. Wait for the green man. Caution: coffee is (not surprisingly!) hot. Don’t use heavy machinery under the influence. The world is full of don’ts, health and safety warnings and protection measures designed to keep us safe, keep us healthy and – perhaps most importantly for those with the signs – to keep us from suing. For the most part this isn’t a bad thing. I can’t help but think that keeping myself breathing, walking and functioning in at least a semi-normal manner is generally a sensible idea. But what about those times when you want to be reckless, live on the edge, take some risks and give yourself a fright? Are there still places in this city that let thrill seekers get a kick, despite living in this world of health and safety nuts and compulsive worriers? The answer is absolutely yes, there are plenty of thrilling London experiences for adrenaline junkies…
White Water Rafting
If you thought you needed to head to some dramatic distant location on the other side of the world in order to go White Water Rafting, you would be wrong. You only need to venture outside of the M25, and only by about a mile.
The Lee Valley White Water Rafting Centre was built to host the 2012 Olympic Canoe Slalom competition, but is now open to the public and is one of London’s best spots for thrill seekers.
For experienced paddlers who can meet the Centre’s competency tests it is possible to enjoy the white water rapids on your own. For those without a history of negotiating a way through high waves and whirlpools and risking drowning as a hobby, you can jump in a raft with up to 8 others for a white water experience.
Up at Lee Valley £49 will get you a safety briefing, a helmet, a life vest and four to six runs down the Olympic Course. With each run your guide makes the route more difficult, wetter and more exciting as you wildly attempt to keep the raft on course whilst it constantly threatens to tip over and send you into the drink.
http://www.visitleevalley.org.uk/en/content/cms/london2012/lee-valley-white-water-centre/
Up at the O2
Having only opened in June, ‘Up at the O2’ is set to be one of London’s premium adrenaline attractions. The 90 minute experience involves ‘climbers’ journeying from ‘Base Camp’, at ground level, up and over the roof of the O2 arena via the 52m summit.
Once briefed, strapped into a harness and with the disclaimer signed (“we faithfully promise not to sue if we fall off..”), you are led to the start of a suspended tarpaulin walkway. Clicking in your climbing device to a metal guide rope you ascend the bouncy pathway to the summit of the famous London landmark and former white elephant. The initial slope is a steep 28 degrees, before levelling out in sections towards the top.
At the top of the world’s largest single roofed domed structure (that’s right, fact fans!) you are given panoramic views of London, with what must be the best views of Canary Wharf from anywhere in the city.
The final part of the descent is, at 30 degrees, even steeper than the first climb; and with changing weather when we visited, the conditions were turning the walk into a slippery and seemingly dangerous adventure. The risk of slipping is real, and whist the climbing equipment will definitely keep you safe, imagining the worst – falling, quickly gathering speed as you slide down the curved roof of the dome and smashing into the floor! – is more than enough to encourage you to keep those footsteps steady!
http://www.theo2.co.uk/upattheo2
Ice Climbing:
It would be easy to conclude that maintaining a hobby of ice climbing and living 
in London are two incompatible activities – but you would be wrong. Located in Covent Garden, the Vertical Chill Ice Climbing wall is one of just three in the UK. Hidden at the back of the brilliant outdoor shop Ellis Brigham the two storey wall is kept at -5˚C and is open to beginners and seasoned professionals alike.
You are provided with a warm jacket and trousers, then an assortment of worryingly sharp points. The crampons have eight spikes each; add two ice axes and you are transformed into a walking talking spiky danger thing. As your instructor explains the various techniques it occurs to you that falling, legs flaying and arms waving, it is very possible you might end up stabbing yourself! No one wants their eulogy to mention that their last action was the creation of several self-inflicted puncture points… But then again what better incentive to stay on the wall and keep climbing up!
http://www.vertical-chill.com/vertical-chill-london.htm
RIB
There are many options for those wanting a boat tour on the Thames. 
But if you fancy something a little more exciting than sitting next to a Saga day trip, and listening to a desperately unfunny tour guide’s regurgitated jokes, then the RIB boat is for you.
The Thames RIB (Rigid Inflatable Boat) Experience is a superfast speed boat tour of that will whizz you past London’s most famous water side attractions – perfect for the time-poor, you can see a host of tourist hotspots in under an hour, and there can’t be many other ways to pull ‘Gs’ as you fly past Canary Wharf! Add to that some genuinely funny and banter-loving guides (and the possibility of whole boat hire) and the Thames RIB tour is perfect for the adrenaline tourist.
http://www.thamesribexperience.com/index.php
Wakeboarding
Any sport that might result in you submerged in the London section of the River Thames, with the possibility of a stomach pump, might be considered extreme. But coming from a combination of skiing, skating and snowboarding, cable wakeboarding gives a whole different splash on things!
Think water skiing, but instead of following a boat, at Wake Up Docklands (under the towering Emirates Air Line cable car: http://www.tfl.gov.uk/modalpages/23828.aspx) you hold onto an suspended cable which accelerates away from you, allowing you to pick up speed and shoot around the course of ramps, jumps and obstacles. The pro’s make the whole thing look easy but if you can keep upright on your board, flying over the water is exhilarating. Try and jump and risk crashing out; but pull off a trick and you can retreat to the bar for high fives and a cold beer.
http://www.wakeupdocklands.com/
Written by Ben Wallace http://www.wherethatbenwent.com/