You can get them in b&q among other places, they come in different powers and colour temperature. Warm white (2700k) is the closest to the normal downlighter but still a little pale. The higher power ones are a tight squeeze in many downlighter fittings.
B&Q recently had a special offer for three downlighters with 9W bulbs for 20 euro thats the cheapest way to get them.
The 9W is equivalent to about 35w bulb .. 11W is close to 50w
You can get 11W versions too they are pricey at about 13 euro and may not fit ..
If you're happy with them I would suggest you buy them on ebay .. much cheaper that way.
Megaman also make a dimmable version .. very pricey about 14 euro in bulk.