Uncertainty surrounding the terms of the 21-month Brexit transition period is among the top risks of the UK's impending departure, a senior European official has conceded.

Valdis Dombrovskis, the European Commission’s vice-president for financial stability, financial services and capital markets union, told delegates at the City Week conference in London on Tuesday that "remaining uncertainty" about the transition period and the final withdrawal agreement was "the first risk" that European policymakers were monitoring.