Alberto Costa resigned as an unpaid aide to the Scottish secretary after tabling an amendment to ensure millions of people are protected, even if the UK crashes out of the EU with no agreement.
Downing Street denied that Mr Cost had been sacked, but the 3million group, representing EU citizens in the UK, condemned the departure as “a disgrace”
It said the prime minister had called their fears “its number one priority”, tweeting: “Now @AlbertoCostaMP gets sacked for wanting to achieve exactly this even in a case of no-deal. And the Govt wonders why we don't trust it.”
Earlier, Mr Costa, the Scottish-born child of Italian migrants, tweeted that it was “brilliant” that more than 140 MPs had backed his move, to be debated later on Wednesday.
“This issue transcends party politics, we are not dealing in borders or backstops, but people's lives and their livelihoods,” he tweeted.
“I have been hugely encouraged by the messages of support and hope received from thousands of EU citizens in the UK & UK citizens abroad.”
Many MPs were astonished that Mr Costa had been forced to quit despite several cabinet ministers openly defying collective responsibility over Brexit policy.
However, a Conservative spokesman said Mr Costa had gone because of a “long-standing convention” that aides cannot table amendments in the Commons.
“He’s resigned from the government. Clearly this is an issue he feels very strongly about,” he said.
“You’ll see the government won’t be opposing that particular amendment and the prime minister thanks him for his service.”
It is designed to be attached to be attached to the latest Brexit motion being debated by MPs today, amid the continuing crisis over EU withdrawal.
It demands that, even if there is no-deal, the citizens' rights part the withdrawal deal is carved out and approved as a separate treaty, to ensure millions of people are not left high and dry.
When Jeremy Corbyn urged the prime minister, on Tuesday, to accept the amendment, the prime minister suggested it was pointless, because the rights of British ex-pats were a matter for individual EU countries.
Ms May has already promised to protect the 3.2m EU citizens in this country – although they are seeking the stronger guarantee offered by the Costa amendment.
Mr Javid told a committee of MPs that the government would support Mr Costa’s amendment because it was “a reasonable question to ask”.
However, the spokesman’s suggestion that the Tories “won’t be opposing” it hints at abstaining – rather than supporting.
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