Just hopping onto the thread with some info about the averages being used throughout.
£29.6k was the median average in 2017, for full time workers.
The latest full data set is the ASHE tables from 2017 which can be found here:
www.ons.gov.uk/employmentandlabourmarket/peopleinwork/earningsandworkinghours/datasets/annualsurveyofhoursandearningsasheguidetotables
Well, that's the guide and then you can download the full dataset to review in excel. They have information on average salaries for full and part time workers, male and female, different age groups and different occupations as well as different areas of the country.
I attach a snip of the full time gross annual wages dataset - showing the median (for full time) at 29.6k in 2017.
The mean (for full time) is much higher. Part time workers bring this down a chunk, but given we can't assess from the data set whether part time workers are part time through choice or through being unable to obtain more work and because the part time workers aren't presented annual using a pro rata wage, it's not terribly usable for comparison.
You can see here that 50% of full time workers earn more than £29.6k and 50% earn less.
The interquartile range is 21.2-41.7k, so half of people earn between those two sums. 25% of full time workers earn less than 21.2k, and 25% earn more than 41.7k. When you consider how variable average wages are across the UK it's quite plausible that some people will either know very few people earning more than the average or very few people earning less. It doesn't, however, change the median (for full time wages).
I think one could probably do something interesting with the hourly wage data from that dataset but I haven't had enough time recently to play with it to do any calculations - this will be especially key when you consider that anything >30 hours per week is considered full time. I don't believe the information above includes overtime payments though.