Major City firms will start implementing their Brexit contingency plans at the end of the year unless there is an agreement about the UK’s transition terms for exit from the EU, according to the City regulator.

Financial Conduct Authority chief executive Andrew Bailey said City firms were getting near to the point where they would have to take steps to move staff and other measures to ensure that they can continue to operate seamlessly once the UK leaves the EU in March 2019.

He made his remarks amid expectations that Wall Street firm Citi will announce that Frankfurt is to become its key hub in the EU. The bank employs 9,000 people in the UK, and its senior management revealed in January that they were using 25 criteria to help them decide which financial centre to chose for its EU centre.

A formal announcement from Citi is expected on Wednesday about what steps it will need to take to keep conducting sales and trading activities if it loses the key “passporting rights” it currently uses to conduct business across the EU. These passporting rights mean that banks can operate out of London in other members of the EU without the need for extra regulatory approval.

James Cowles, who runs Citi’s operations in Europe, the Middle East and Africa, said in January: “Our issue is with our broker dealer, which is located in the UK and will lose, presumably, passporting rights.”

It is thought that up to 200 roles currently based in London could be affected.

Citi has talked to regulators across the EU – Ireland, Italy, Spain, France, Germany and the Netherlands – as it already has operations in 21 of the 28 countries.

The Bank of England called on hundreds of City firms to submit their Brexit plans by 14 July, and Bailey is warning that they may have to be implemented at the end of this year if they are to have enough time to complete their preparations.

“By the end of this year, their plans tell them that in order to have things in place, they’ve got to implement them,” said Bailey. Without a transition agreement, they will be having to do so without knowing the outcome of the negotiations. Firms were not moving their business yet, he said, but they were talking “more in terms of getting there”.

Last week, Barclays said it talking to regulators in Dublin to discuss expansion, while JP Morgan has also been discussing plans with regulators in the Irish capital. HSBC has warned it could move 1,000 staff from London to Paris.