Skimming through Legal Cheek's articles regarding NQ pay, I've noticed that firms (especially UK based ones) tend to increase salaries every 2 years approximately.
For e.g.: there were sizeable increases amongst MC NQ salaries in 2017 and 2019 to keep up with competition from US firms.
Of course the pandemic has impacted this greatly, with firms cutting salaries. Furthermore, this is just an observation of a trend, and US based firms in London are often the trendsetters with regards to pay (and have been for a long time).
For example, now defunct US law firm Bingham McCutchen became the first firm to pay NQs a base salary of £100,000 back in 2010 (
https://www.thelawyer.com/issues/15-february-2010/bingham-shocks-market-with-nq-salary-of-100k/), prompting MC firms to up their pay to remain competitive in acquiring the best talent.
In this fashion, US firms will continue to set the benchmark for pay in the London legal market, with UK firms almost always following suit afterwards. But please do keep in mind that there are many factors that go into pay increases, and UK and US based firms have distinct business models, partner compensation structures, and practice area strengths.