United Kingdom Conservative Health Minister David Prior expressed his regret for the Brexit and called on Prime Minister Theresa May to fight to remain in the E.U.'s single market last Thursday, the Independent reported.

The parliamentary under-secretary of state for health in the House of Lords made his remarks at the Royal College of Physicians’ annual dinner in London. He warned an audience of 170 doctors that the U.K.'s vote to leave the E.U. could impact the country's access to medical, scientific and academic personnel throughout Europe.

“My personal view is that leaving Europe was a terrible mistake. But given that it was a mistake, we must do everything we can to ensure that we stay in the single market and that we do have access to the best people from around the world," Prior said.

Many MP’s within the Conservative Party supported the "Leave campaign" during a June referendum determining whether the U.K. would remain part of the E.U. However, a majority, including former Prime Minister David Cameron, Secretary of State for Communities Sajid Javid and former Chancellor George Osborne, voted to remain. Following the referendum's results, many politicians are attempting to soften the blow and retain some crucial E.U. privileges.

“Lord Prior’s remarks are starkly at odds with his own government, which is veering towards a reckless and divisive hard Brexit,” Liberal Democrat leader Tim Farron told the Guardian.

“Theresa May must stop pandering to the views of a minority of hardline Tory Brexiteers and start standing up for the national interest. A disastrous exit from the single market would leave us all poorer.”

May, who voted to remain, insists on a “Hard Brexit,” meaning loss of access to the E.U.’s exclusive single market. The single market is defined as “one territory without any internal borders or other regulatory obstacles to the free movement of goods and services.” Without this market, the U.K. faces a significant increase in trade barriers such as tariffs, visas and regulations that are bypassed between members of the E.U. One think tank, Civitas, has estimated the post-Brexit cost for E.U. companies doing business with the U.K. to be nearly $16 billion, while costing U.K. companies over $6 billion.

The steep costs could lead businesses and financial institutions to flee London, taking with them vital capital from the U.K. and its economic infrastructure. Chancellor Phillip Hammond told parliament Tuesday that he vows to keep the financial sector “at the heart” of negotiations with the E.U.