To be honest I thought the UK was still third in the EU economy top N (behind FR and DE). UKoGBnNI and FR have vied for the same position for quite a while now.
Another interpretation is that we have equally successful economies based on one, rather archaic but generally agreed on, measure.
> This year will be the first time since 2013 that France has topped the U.K. in the ranking, according to the IMF.