“Brexit has introduced uncertainty. I think the change of administration in the US has introduced an even bigger piece of uncertainty for the European Union,” Hammond said in a panel discussion about the EU in the Swiss resort of Davos.

Hammond, a former foreign minister, said EU countries varied widely in how big a security threat they saw from Russia.

“Anything that changes the settled status quo of a Europe that lives with Russia as a neighbour, but lives under a protective US security umbrella as it does... will play into the dynamics of the European Union,” Hammond said.

Trump, who is due to be inaugurated as US president later on Friday, has expressed his admiration of Russian president Vladimir Putin, and raised concern about how countries share the cost of providing security via the NATO alliance.