By Stephen Jewkes and Kylie MacLellan
MILAN/LONDON (Reuters) - A European Union without Britain would be "impossible", Italian Prime Minister Matteo Renzi said on Wednesday, after talks with Prime Minister David Cameron about his plans to reshape Britain's EU ties before an in-out membership referendum.
Ireland said it had begun contingency planning for a British exit from the EU.
Cameron, re-elected last month, is due to present his reform plans in more detail at an EU summit in Brussels next week and hopes to hold preliminary talks with EU leaders before then.
"For us it is a priority (that) the UK can continue to work inside the European Union because a European Union without the UK is impossible," Renzi said, after lunch with Cameron in Milan.
Cameron, who has pledged to hold the EU referendum by the end of 2017, said the two leaders had "common perspectives" on issues such as boosting the bloc's economic competitiveness.
Britain is seeking changes to EU treaties, which it says are needed to achieve reforms to EU migrants' access to welfare payments.
"Across the areas that we are looking to address, they want to work with us to find solutions," a spokeswoman for Cameron said.
IRISH CONTINGENCY PLANS
Cameron will head to Luxembourg for dinner with Prime Minister Xavier Bettel later on Wednesday. On Thursday, he will discuss his reform plans with both European Parliament head Martin Schulz and Irish leader Enda Kenny in London.
Ireland's Minister for European Affairs Dara Murphy told BBC Radio on Wednesday his country had begun contingency planning for a British exit from the EU.
"The core focus at the moment is the strategy around the negotiation to play a part in keeping the UK in the European Union," he said.
"But, yes, it would be remiss of us given the possibility that our largest trading partner ... may be exiting the European Union, that is something we, of course, are looking at."
Having met with more than half of EU leaders so far, Cameron has received a mixed reception. German Chancellor Angela Merkel pledged to work to clinch a deal that would keep Britain in the bloc, but British newspapers reported his plans were rebuffed by the leaders of Spain, Finland, Romania and Belgium.
On Thursday afternoon Cameron will travel to Slovenia to meet Prime Minister Miro Cerar, before heading to Bratislava on Friday where he is due to hold talks with the leaders of Slovakia and the Czech Republic.
(Editing by Andrew Osborn and Ralph Boulton)