What's so funny about it is that it's not likely true. What would be true is that 49 percent get less than the mean.
Think you have that flipped. The median is the 50th percentile. The mean is the average.
Median would definitely be true. In fact, it's quite likely that more than half are below the average/mean as well, since the distribution is probably a bit skewed. Just as all but one of the people in a room will be below average income when Bill Gates walks in, most Britons are probably below average because of a few high-bandwidth folks pulling the average up.