Well yes... but that includes internally displaced
https://www.unhcr.org/uk/figures-at-a-glance.html
So going by the unhcr figures it's 20.7 million that were Internationally displaced and looking for a new country
So the uk took 0.98% which when you consider the uk has around 0.87% of world population is I would suspect better than most countries
Plus consider people who have come in illegally will not be in the 20,399 figures and it can be argued the uk is more than pulling its weight on a per capita basis.
As you say an overhaul at un level would probably be the best starting point... and making a system that can cope with potential future climate migration but let's be honest that's not gonna be easy or achieved quickly