LONDON - Britain's Brexit bill, the subject of a furious row this week between Brussels and London, will not pose a "big threat" to public finances, the government's fiscal watchdog said Thursday.

"A lot of attention focuses on the possible divorce bill, but, while some numbers mooted for it are very large, a one-off hit of this sort would not pose a big threat to fiscal sustainability," read a report from the Office for Budget Responsibility (OBR).

Britain last month kicked off lengthy negotiations with the EU to set the terms of its divorce -- and a potential timetable for discussing a future free trade deal.

The nation's estimated exit bill has however hogged the headlines.

EU officials told AFP that the figure could be around 100 billion euros ($112 billion).

But British foreign minister Boris Johnson declared on Tuesday that Brussels could "go whistle" for the money.

In response, EU Brexit negotiator Michel Barnier warned Britain on Wednesday to quickly settle the row -- adding: "I am not hearing any whistling, just the clock ticking."

Barnier also urged Britain to send Brussels its negotiating position on all key issues ahead of a second round of formal Brexit talks with his British counterpart David Davis, which start Monday in Brussels.

The OBR added Thursday that the conclusion of successful trade details -- with the EU and elsewhere -- were of greater importance than the size of the exit bill.

"More important are the implications of whatever agreements are reached with the EU and other trading partners for the long-term growth of the UK economy, which we do not attempt to predict here," the watchdog said.

"If GDP and receipts grew just 0.1 percentage points more slowly than projected over the next 50 years, but spending growth was unchanged, the debt-to-GDP would end up around 50 percentage points higher."

 

Britain will leave the EU in March 2019 after voting in a shock referendum last year in favour of its departure.