British Prime Minister Theresa May’s position in the Conservative party would be “difficult” if she agreed in Brexit negotiations to anything that resembled a customs union with the European Union (EU), a former U.K. trade minister said Wednesday.

Francis Maude, senior adviser at Covington and once a Tory lawmaker, said that a customs union with the EU would make it hard for Britain to negotiate trade deals elsewhere.

“I think Theresa May’s position would be extremely difficult in the Conservative party if she were to agree to something which effectively amounted to bring in the customs union or something very close to that,” he told CNBC’s “Squawk Box Europe.”

“There’s not an easy answer. The customs partnership looks pretty difficult to me. I don’t see that the EU would agree to that and Britain able to cut its own trade deals in the future.”

Maude said that increased use of technology could be “the better bet” to allow goods to travel freely between the U.K. and the EU trading bloc, a strategy recommended by some Conservatives.

He also criticized the EU for asking British negotiators to find a better solution to the Brexit impasse.

“The (European) Commission is saying no. That’s not on. They’re saying it doesn’t work,” Maude said. “Quite often on their position on Brexit is that they stake out a fact and say it’s not a possibility when all they really mean is that they’ve decided that they don’t want it.”

He urged the 27 EU member states to find a “sensible, pragmatic deal with goodwill on both sides.”

Maude’s own view on the 2016 Brexit vote is somewhat unusual. He wrote on a Tory blog last year: “I took no part in the referendum campaign — I thought both sides massively exaggerated their case, and thought a vote to leave would mean some short-term economic downside through uncertainty.”

May’s Conservative party is deeply divided on whether there should be a future customs union with the EU. Trade Minister Liam Fox opposes any form of a customs union.

As the prime minister navigates complex Brexit negotiations, she was dealt another blow with the resignation of one of her closest allies Sunday. Home Secretary Amber Rudd quit her post after the government faced increasing pressure over the deportation of long-term residents originally from the Caribbean who were wrongly labeled illegal immigrants.