LISBON (Reuters) - Britons living in Portugal will keep their residency rights and tourists won’t need a visa even in the event of a no-deal Brexit, and Lisbon hopes Britain would offer the same benefits to Portuguese citizens, Economy Minister Pedro Siza Vieira said.

Portugal's Economy minister Pedro Siza Vieira speaks during an interview with Reuters in Lisbon, Portugal January 16, 2019. REUTERS/Rafael Marchante

Britain is due to leave the European Union on March 29 but parliament’s rejection this week of Prime Minister Theresa May’s withdrawal agreement with Brussels has thrown those plans into chaos and opened up a range of outcomes, from quitting with no agreement on future relations to halting Brexit altogether.

“At this moment we do not even know what the United Kingdom wants,” Siza Vieira told Reuters in an interview late on Wednesday.

“In the absence of an alternative proposal by the United Kingdom, what every (EU) member state is doing is adopting measures that allow them to react to a unilateral circumstance.”

Even without a Brexit deal, British citizens living in Portugal would retain rights including access to healthcare. “We are ready to do this unilaterally,” he said, adding that he hopes Britain will do the same for Portuguese.

Separately on Thursday, Prime Minister Antonio Costa said airports in the Algarve and Madeira will open separate customs lanes for British tourists to ease entry after Britain quits the EU. There would also be judicial cooperation with Britain.

Britons are the biggest group of tourists to Portugal but their numbers have dipped recently as the pound has fallen against the euro on Brexit concerns. Portugal will launch a promotional campaign in Britain in an attempt to offset this, the economy minister said.

Portugal and Britain are the world’s oldest allies, forged through a 1386 treaty.

A tourist boom has boosted Portugal’s economy after its 2010-14 debt crisis and Siza Vieira predicted tourist numbers would continue to rise, albeit at a slower pace.

“We...assume that tourism will continue to grow, though probably not at the same rate as in recent years - Portugal was one of the tourist destinations that grew the most in recent years,” he said.

A record 13 million tourists arrived last year.

Siza Vieira said he expected further expansion in investment, a motor for growth in recent years, including attracting companies from third countries which might previously have considered Britain as an EU center.

“We are seeing growth in investment with European origin, but also American and from various parts of Asia,” he said.

State-owned China Three Gorges is bidding for utility EDP, Portugal’s biggest company by assets, while other Chinese firms have bought large stakes in electricity grid REN, insurer Fidelidade and bank Millennium bcp.