City investors predict the value of one pound will slump below one euro if the UK leaves the EU without an agreed withdrawal deal — as Theresa May heads to Brussels again today to try to secure one.

The pound has been climbing in recent weeks, from a 12-month low of €1.10 hit in late August up to its current value of €1.14. But £1 to €1 is a realistic possibility if the current deadlock in the exit talks persists through to March next year, fund managers believe.