Kate Hoey has accused the Conservative Party of "betraying" Northern Ireland with its Brexit deal.
Taking aim at the Northern Ireland protocol, the 'Irish Sea Border', the effects on the second-hand car market and other issues, the County Antrim-born peer said the words 'and Unionist' no longer apply to the name 'the Conservative and Unionist Party'.
Ms Hoey is a fierce Eurosceptic and frequently rebelled against her former party, Labour, during Brexit negotiations and votes in the Commons.
In July 2019 she announced she was retiring from the Commons and would not seek re-election as a Labour candidate, later putting her support behind the DUP in the general election in Northern Ireland that December and endorsing the Tories.
She was made a life peer in September 2020.
Writing in the Daily Telegraph, Ms Hoey said Secretary of State Brandon Lewis's claim that there is no trade border down the Irish Sea "puts in mind the joke about the emperor with no clothes".
She said Michael Gove caused anger among unionists by not guarding their interests, pointing out no one in Northern Ireland voted to change the constitutional position of the region.
"The 44% of people in Northern Ireland who voted for Brexit voted for the UK to leave as it stated on the ballot paper, not for some of the UK to leave and certainly not to find the province left to the diktats of Brussels," she said.
"Even among Remainers, most did not want economic and societal barriers within their own country, the UK. Bluntly, the Northern Ireland protocol signed as part of the Withdrawal Agreement has shown that, when it suits the Government, Northern Ireland can be sacrificed."
Under the agreement with Brussels, Northern Ireland is still bound by many EU rules, such as those in ports. This has resulted in reports of lorries being held up before they were due to cross the Irish Sea because of incorrect paperwork.
Ms Hoey said this shows Northern Ireland was becoming "a place apart" and extra rules, such as those on pets coming here from GB.
She also criticised the effect the Northern Ireland protocol could have on the second-hand car market, as now VAT at the usual 20% rate was being charged on the amount paid by a dealer for a car from Britain, instead of just the amount of profit they make from it, as was the case before.
"These are just a few examples of the way, drip by drip, Northern Ireland is being separated from the rest of the UK. This is happening under a Conservative and Unionist Government," she added.
"Many were fearful of a Corbyn-led government, citing his support for the IRA. Yet there is no way he would have dared put through this betrayal. If he had tried, there would have been no louder howls of outrage than from the Tory opposition.
"Yet a Tory government caved in to an Irish government which in turn was devotedly loyal to the EU. A border between Northern Ireland and a foreign country - the Republic of Ireland - was unthinkable but it was acceptable to put one between the province and Great Britain."
Concluding, Ms Hoey said every Conservative needs to ask themselves: "What has a law-abiding Northern Ireland citizen done to deserve being treated differently to their fellow citizens in the rest of the country?
"Why did years of terrorist violence against them, and the threats of its return, matter more than voting? Why is the Conservative and Unionist Party only Unionist when it is in Opposition?"
The Conservative Party has been contacted for a comment.