The party of Gerry Adams, who was succeeded as leader by Mary Lou McDonald earlier this month, has been urged to “defend the interests of the island of Ireland”

Sinn Fein is under intense pressure to rip up its century-old policy of not voting in parliament to defeat Theresa May’s plans to pull Britain out of the EU’s customs union.

In a public challenge to republicans, Leo Varadkar, the Irish prime minister, called on the party to take its seats in Westminster to “make things better for Ireland”. His comments were backed by Brendan Howlin, leader of the opposition Labour Party, who said it was time for Sinn Fein to “step up to the plate and defend the interests of the island of Ireland”.

Sinn Fein has never taken up seats in Westminster since its first MPs were elected in 1917. They still refuse to swear allegiance to the Queen and do not