Keir Starmer has been accused of plotting a “genuine sell out” to the European Union by Britain’s former Brexit negotiator. The warning comes after the Prime Minister refused to make a key guarantee about his planned Youth Mobility Scheme with Brussels yesterday.

Speaking in Albania, Sir Keir Starmer repeatedly refused to guarantee that the planned free movement sell out will see the number who can participate each year capped. Brussels has been resisting calls for a cap by Britain’s Home Office, who are concerned about the damage an uncapped scheme would do to their plans to bring down net migration. The proposed scheme would allow EU citizens under the age of 35 to come to the UK to work or study, possibly for up to four years.

He merely said: “We have to respect the outcome of the referendum and that’s the framework in which we have been negotiating.”

Reacting to the failure to guarantee a cap, Britain’s former Brexit negotiator Lord Frost warned such a deal would be a “genuine sell out”.

He fumed: “The Government has been so dishonest about its approach that it's entirely possible this is expectation management - they *have* agreed a cap and just want to present it as a negotiating triumph.”

“But a mobility deal without a cap would be a genuine sell out. There are about 80 million Europeans in this age range. However tight the conditions, it would risk opening the flood gates.”

Labour is facing widespread attack from Brexiteers over their Youth Mobility Scheme plan, which they initially strenuously denied they were negotiating.

Three weeks ago, shadow Home Secretary Chris Philp blasted: “Be in no doubt, this is just another attempt by Labour to betray Brexit and reopen the door to uncontrolled and unlimited immigration. Every time Labour negotiates, Britain loses.”

Meanwhile, former home secretary Suella Braverman, an ardent Brexiteer, told the Express the planned sell-out is merely the “thin end of the wedge”.

She warned: “The British people voted to take back control and end free movement of people. This agreement is the thin end of the wedge and the continuation of the Brexit betrayal.

“Labour never accepted the result of the referendum and are determined to see us return into the clutches of the European Union by stealth.”

Former business secretary Sir Jacob Rees-Mogg added: “This is part of Labour’s attempt to get the UK back into the EU, but it is giving free movement a different name in an attempt to con British voters.”

He warned: “The Conservatives must promise to annul any deal of this kind and control migration regardless of where it is coming from.”

Speaking to The Sun, Sir Keir also refused to rule out “dynamic alignment” on standards, which would see the UK accept Brussels laws without any say over them.