London’s mayor Sadiq Khan has called for a Brexit transition deal to be laid out to help businesses make plans to stay in London and the UK.

Speaking to the BBC, the Labour mayor said companies are not bluffing when they threaten to move operations from London. He said uncertainty over the UK’s exit from the European Union (EU) is causing issues.

Khan was asked about comments Goldman Sachs’ chief executive, Lloyd Blankfein, made last week. Blankfein tweeted that he will be spending a lot more time in Frankfurt.

Khan said:

He’s articulating publicly what many CEOs and investors who love working in London have been saying privately, which is that unless they have certainty about what happens after March 29 2019, they have got to make a plan B. He’s not bluffing. When I speak to businesses each day, they’re not bluffing.

Read more: These are the companies that could leave the UK after Brexit

Time is running out for a deal

Khan’s comments come the same day Britain’s five biggest business lobby groups are teaming up to request an urgent Brexit transition deal to save jobs and investment in the UK.

The lobby groups, including the Institute of Directors and CBI, are sending a letter to Brexit secretary, David Davis. The letter will say that time is running out and a deal is needed imminently.

According to Sky News, which has seen the letter, it will say:

Agreement [on a transition] is needed as soon as possible, as companies are preparing to make serious decisions at the start of 2018, which will have consequences for jobs and investment in the UK. It is vital that companies only have to undertake one adjustment as a result of the UK’s withdrawal, not two. And that businesses, the UK government and authorities in the EU have enough time to make the changes needed to deliver Brexit successful.

Last week, financial lobbying group TheCityUK said the value of a Brexit transition deal is “disappearing by the day”.