where can i buy hydrogen peroxide to whiten my teeth in the UK? and what percentage should i look for?

people say i should look for 3%, but crest whitening strips have 10% hydrogen peroxide in them? please help someone!!!
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I used to buy H. Peroxide at an ordinary chemist here in London, the old fashion chemist, I don't think the big chain pharmacy will sell it. The chemist I used to buy it from used to sell it "by the quantity" what I mean is he asked me to bring the empty bottle or to buy an empty bottle from him. He used to have the solution at 10% but I used to ask him to dilute it down to 3% by adding purified water. For your teeth start at 3% and try few times, if no problem it seem you can go up to 10%. Be careful with your gums as the peroxide will "burn" a bit on the gums. I have only tried a few times and didn't see any result. I can't tell you if it is safe practise. I also found this on the web, but try to search more and read to get a better idea. http://hubpages.com/hub/Hydrogen-Peroxid…
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