London is notorious for low SWEng salaries; you might not have any other choice than to contract somebody in Ukraine who didn't escape somewhere else if your own employees get higher paid remote gigs in the US...
I was actually going to challenge this before I did a bit of research and discovered you're right - the average wage for a software engineer is £47,500 (https://www.cwjobs.co.uk/salary-checker/average-it-salary). That's ugly.
I'm from Liverpool originally (live abroad now) and I have friends in Manchester earning £50-60k... in the North of England. That's a big wage in that area.
[0]: https://www.cwjobs.co.uk/salary-checker/average-software-eng...
72k in London isn't a lot :)
With the banks and big tech, I'm pretty sure it has the highest paying SWE salaries in Europe.