The Scottish Tory pilloried his SNP colleague for accusing the UK Government of planning to take over all repatriated powers after Brexit.
Lord Forsyth, who served as MP for Stirling for 14 years, said: "This is just such nonsense. This is a party that says they want decisions that affect Scotland to be made in Scotland.
"But they are actually arguing they’d prefer our fishing policy and our agriculture policy to be decided in Brussels rather than being brought back in the United Kingdom."
Lord Forsyth slammed Blackford's claims branding the SNP's Brexit plans "perverse"
"On the point of devolving fishing: in order to make treaties with other countries, in order to control our fishing waters, you need to be a nation-state and the nation-state is the United Kingdom!
"And the people of Scotland voted to keep it that way."
Lord Forsyth also took a dig at SNP's attempts to thwart the Government's decision to leave the single market and the customs union as part of Brexit with threats of independence.
He said the Scottish party was "perverse" to even consider risking the close ties it shares with the UK to maintain a good trade relationship with Brussels.
Speaking to BBC Any Questions? he said: "The Scottish Nationalist Party want to leave our biggest single market, which is the rest of the United Kingdom where 68 per cent of our exports go to.
"Our exports to the European Union single market is 16 per cent. It is a perverse position!
"This is a party which had the largest percentage of people voting to leave the European Union in its membership in the referendum."
A new opinion poll recently revealed a damning verdict on the SNP after a decade in power.
It found that 42 per cent of Scottish voters disapprove of the Nationalist’s record to date while 39 per cent approves of the party's 10 years in government. Another 19 per cent did not know.
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