I'd suggest getting something sooner rather than later, so you have plenty of time to familiarize yourself with the light, not to mention test it out properly against production defects. I don't know how 100 pounds/franks or whatever that is relates to dollars, but I'm guessing the more reliable brands like Surefire are probably out of your price range.
Since you're posting using a non-US currency, I'm also guessing that the selection you have available where you're at might differ from the US. And, considering how you can routinely buy Blu-ray sets that go for over $100 at amazon (US), for as little as $25 at amazon (UK), I imagine your costs might be a lot different from what we'd have to pay in the US too.
But, if durability and waterproof ratings are of significant importance, the only real game in town that's still relatively affordable would appear to be Armytek. No other light manufacturer that I know of claims 10-30 meter impact resistence (10 meters for headlamps, 30 meters for most everything else) and 10 meter/30minute waterproof rating, and claims to back it up with a 10 year warranty. Some of your custom makers and such are said to be just as durable or even moreso. And Surefire is known for their trouble-free warranties. But, from what I've seen they're a lot more pricy too, and the best warranty isn't of much use, if you need a light NOW, rather than waiting on a repair. Most light manufacturers only quote the industry standard for impact and waterproof ratings, which is about 1.5 meters impact and 3 meters waterproof. Many don't even quote that, and I wouldn't trust any of them to actually survive a 1.5 meter fall, nor their manufacturers to fix them if they don't. Some light manufacturers are not even set up for repairs. If the product clearly fails within the warranty window, they simply ship you a new light. But, that only covers clear manufacturing defects. If the light went out due to being dropped or drowned, it's not covered, regardless of whether you claim it happened within the resistance window. Armytek and more expensive brands being the only exceptions I'd trust, and I haven't had to deal with Armytek's support as yet, so I don't know how well I can trust them for certain. I only know that people who actually live in Canada have praised their post-purchase support.
Of course no flashlight maker is immune to manufacturing issues, so the safest way to go, is to bring at least two lights, should something happen to one, which might mean buying an even cheaper brand, like Convoy, which is one of your best value for the money light makers, especially when they're on sale.