In 250 of 391 United Kingdom local authority areas, Baby Boomers outnumbered Millennials in 2016. But Millenials are concentrated in more populated areas, so they outnumbered the Baby Boomers: 16.2 million to 14.6 million. There are many different definitions for these groups but the ones I use here both have 19 separate annual age cohorts in them. Using this definition. Millennials turned 16-34 in 2016 and Baby Boomers turned 52-70.
Alasdair Rae, 2018