LONDON (Reuters) - Australia said on Monday it would be open to the idea of Britain joining the Trans-Pacific Partnership regional trade group after it leaves the European Union.

FILE PHOTO - Australian Foreign Minister Julie Bishop addresses the 72nd United Nations General Assembly at U.N. headquarters in New York, U.S., September 22, 2017. REUTERS/Shannon Stapleton

But Julie Bishop, visiting Britain as Prime Minister Theresa May tries to unite her cabinet on what they want from Brexit, also said Australia would only be able to strike a bilateral trade deal with Britain if London sticks to its plan to leave the EU’s customs union.

“We would of course welcome interest from an economy the size of Britain’s,” she said in response to a question about Britain joining the TPP after delivering a speech at the Commonwealth Bank of Australia in London’s financial center.

British trade minister Liam Fox said earlier this year that joining the Trans-Pacific Partnership was an option for the country after Brexit.

The 11 TPP countries - which include Japan, Canada and Mexico as well as Australia - are due to sign their agreement in March. U.S. President Donald Trump pulled the United States out of the group soon after taking office, but he said in January that Washington might yet stay in.

Trade economists say Britain is unlikely to make up for losses incurred by leaving the EU’s single market and customs union by striking bilateral trade deals with other countries. The EU already has trade agreements in place or awaiting ratification with most TPP countries.

WHEN THE TIME IS RIGHT

Bishop said Australia was keen to pursue a bilateral free trade agreement with Britain, when the timing was right.

She said a bilateral deal could only happen if Britain went ahead with its plans to leave the EU’s customs union - a move opposed by British businesses.

“Australia is very keen to pursue a free trade agreement with the United Kingdom. I think that would be precluded if the United Kingdom were to rejoin the customs union,” she told reporters.

Leaving the customs union would leave Britain free to pursue its own bilateral trade deals. But the EU has said that would make border checks between Northern Ireland and the Irish Republic inevitable - a major obstacle in Brexit talks.

Bishop said Australia would want to secure rights for its citizens to work in Britain as part of any deal with Britain.

She declined to comment on a major rift that opened up in Australia’s fragile ruling coalition after Deputy Prime Minister Barnaby Joyce refused to quit over an affair with a staff member,

Asked if she was confident that Joyce and Prime Minister Malcolm Turnbull could rebuild their working relationship, Bishop referred only to earlier comments from both men they were committed to working together.

Bishop is due to travel to Budapest to meet officials from Eastern European countries. She said she intends to raise with Poland its judicial reforms that the EU says undermine the independence of Polish courts.