Ireland's deputy prime minister has said the UK should seek the "closest possible" alignment with the European Union's customs rules after Brexit.
Simon Coveney's intervention comes amid divisions at the heart of the UK Government over the extent to which Britain will diverge from Brussels after leaving the EU.
The Tanaiste and foreign affairs minister used a speech in London to urge Theresa May's administration to "reflect carefully" on which Brexit options would secure prosperity.
His comments come after Chancellor Philip Hammond caused a storm within Tory ranks for suggesting the UK might only move "very modestly" away from Brussels rules.
Mr Coveney told the Chatham House foreign affairs think tank: "Ireland needs and wants a happy and prosperous UK, I hope the British Government and Parliament will reflect carefully on the path to that prosperity over the weeks to come.
"The most successful single market and customs union in the world - a market UK genius helped design - that market is on your doorstep.
"The British economy is integrated wholly into it, and gains from access to it to a degree that will be impossible to replicate from future UK-only trade deals with third countries.
"The EU and UK both stand to gain from the closest possible customs and regulatory partnership.
"And I hope the UK is ambitious in what it seeks in this respect, with an eye to what is achievable and where the EU is coming from."
Mr Coveney also used his speech to back the idea of looking at a bridge between Scotland and Northern Ireland after suggestions of a crossing between Larne and Portpatrick.
"I certainly see no harm in looking at the feasibility of big infrastructural projects to link our islands, if a credible economic case for any initiative can be made," he said.
But he pointed out that "metaphorical bridges are less costly but no less valuable" as he called for increased UK-Irish co-operation to replace the close relationship the two countries currently had as fellow EU members.
While in London, Mr Coveney held talks with Foreign Secretary Boris Johnson.
"The two ministers ... expressed their mutual desire to reach a deal on the UK's exit from the EU that works for everyone, as well as a shared commitment to avoiding a hard border," a Foreign Office spokesman said.