The number of financial services jobs available in the City of London fell by 23% between January and February this year, according to figures by Morgan McKinley Financial Services.
The employment agency said that some businesses had decided to move jobs to other countries in the EU as a result of the UK government sending inconsistent messages about the kind of deal it is seeking post-Brexit.
It is thought to be large institutions in particular that are exercising hiring caution, as they are often hampered in their ability to respond quickly to significant changes in markets and regulations, unlike smaller companies.
Morgan McKinley Financial Services operations director, Hakan Enver, said: "Brexit has pushed institutions into two camps. On one side we've got the 'business as usual' team.
"On the other we have institutions that are tired of the government's hemming and hawing and have already begun to move jobs to other EU countries. It's the latter group that's contributed to the quarter drop in jobs available.
"The implementation of Brexit could take years, which is not a problem for small, nimble businesses that don't need to forecast years ahead. They can adapt in real time, and cross the relocation bridge when they reach it.
"Large institutions, however, are currently using up incredible institutional resources to project years out and plan for a future that changes from one day to the next. For many, it's simply proving easier to get ahead of the worst-case scenario and get out of London now."
The number of financial services jobs new to the market over the last year is shown below:
The figures show a 17% drop in the number of City jobs available over the last year, however a spike in January could suggest that February's dip might not represent a trend.
"There's a chance we'll see a post-Article 50 uptick in April, just as we did post-Brexit," Enver continued.
"But the data suggests that Brexit has had a fundamental depressing effect on City jobs. We've already witnessed, what was a handful of jobs leaving, become hundreds. How long before we're looking at losing thousands, even millions?"
According to 2015 data from CityUK, the relocation of the financial services industry from the UK would cost the economy £176bn a year and 2.2 million jobs.
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