Lloyd's of London is reportedly poised to name Brussels as its new base in Europe.
The announcement by the world's largest insurance market will come less than 24 hours after Theresa May triggered Article 50 with the timing first reported by Sky News.
Lloyd's is shifting some operations to the continent in order to protect revenues generated within the European Union as the UK heads for the exit.
A spokeswoman would not confirm the decision, reported by a number of media outlets, but said a statement would be made on Thursday alongside its annual results.
Lloyd's, which has been in existence for well over 300 years, is among the most important financial services businesses headquartered in the UK.
Thousands of people are employed in the City by it and the insurers which operate there.
Lloyd's disclosed in a statement last week that it was preparing to present further details of its plans to open a subsidiary in the EU.
It said: "It is important for Lloyd's, the market and our customers, that we are able to provide continued access to the EU once the UK formally leaves, but equally, customers in Europe want that same access to the Lloyd's market."
London has been the world's premier hub for specialist insurance and reinsurance for centuries, and Lloyd's is among the City's most prestigious institutions.
Because Lloyd's is a market comprising a range of underwriting syndicates, the move to establish a new EU base is likely to be especially complex.
Chairman John Nelson has previously said that Lloyd's had made a decision to act quickly because more than 10% of its revenues come from within the EU.
Large investment banks are also weighing the future of their UK-based operations, with Sky News revealing last week that Deutsche Bank (IOB: 0H7D.IL - news) had signed a 25-year lease on a new City base.