It is possible that the adjustment is not correct, i.e. the lights are still shining too steep down though the knob is set to 0. Though you can test this on your own, shops will do this with more precision. It doesn't cost much and may be for free.
DucatiKiller suggests high-power bulbs in his comment.
From the legal side (they're for sure illegal in the UK, too), I think the bulbs will never be inspected, but you may still get into trouble. Imagine someone says the crash happened because he was dazzled by your lights...
From the technical side, make sure relays and cables can handle the higher current, an the headlight can handle the increased heat from this bulbs. 65W instead of 50W may be OK, but 110W instead of 55W is quite much.
But there are also legal brighter bulbs out there like for example Osram Night Breaker. Compared to a generic bulb, they claim to give more than twice the light, 40m wider range and 20% more white light (Now, how to measure that???)
This are of course advertisements, and the numbers are suspicious. But to my experience (and many others on the web), they indeed give brighter and more white light. If it's twice the light? Hmmm, not sure, but definitely more. Here is a german blog showing pictures with standard and this bright bulbs.
This bulbs are legal and have no technical issues because they have the same power as generic bulbs. But they also have two disadvantages: They are really expensive, and their life time is typically just about 50% of generic bulbs. The reason is, to get more and more white light out of a bulb with same power, the filament must be hotter. But hotter filament drastically decreases life time.
Finally, you mentioned Xenon lights. It's not that simple to convert normal lights to Xenon lights. You do not only need headlight washers, you will also need an automatic adjustment, and the headlight must be made for Xenons. There are many illegal conversion sets out there. I guess Xenon is usually only an option if the car is available with Xenon from the manufacturer.