Shadow Scotland secretary Lesley Laird accused the Tories and the SNP of “sawing away at the legs that support the union”.
Her warnings came as MPs debated “strengthening the Union” in the Commons.
Ms Laird said: “The nationalist government in Edinburgh and the nationalist government in London are both clear threats to the unity that has historically given this country the strength to work together and which will under Labour have the strength to do so again.”
Ms Laird, in a wide-ranging attack on the Government’s record on everything from Brexit to benefit reform, added: “The Tories are doing what they have done for decades, ripping each other on Europe, fighting for personal power and getting ready to get rid of yet another Prime Minister who doesn’t suit the Brexiteers.”
She went on: “It is hardly surprising that we are missing opportunities to strengthen our union when the Tories clearly don’t understand devolution, never mind believed in it.
“And they are sleepwalking into a nationalist trap because their instinct is to pass the buck and the Scottish Government’s instinct is to draw powers from Whitehall and hoard them in Edinburgh, and undermine local government at every turn.”
She later told the Government: “Your ineptitude, selfishness and brand of politics has played into the hands of those opportunists across there (the SNP).
“Do the Union a favour, do the country a favour, do the millions of people a favour whose lives are worse off under your rotten Government - move over and allow Labour to govern.”
Opening the debate, Cabinet Office minister Chloe Smith reiterated the Government’s duty to “govern for the whole of the United Kingdom” while also acknowledging the development of devolution.
She said: “The Prime Minister’s words show this Government believes this Union cannot and should not be taken for granted.”
Ms Smith said being part of a “bigger, stronger” UK benefits all citizens in the four nations.
She later became a little tongue-tied and mispronounced Scotch whisky while trying to maintain her optimistic tone.
Ms Smith joked: “I’ve clearly already been on the whisky - let me try and start that sentence again.
“I’m going to attempt to get through a sentence that compares Scotch whisky to English ale and Northern Irish scones to Welsh cakes, and I may well get to the end of that sentence with a cheer from the House.
“Whichever one of us has the better cake or drink or more noble history, we are united in our deeper beliefs, our democratic traditions and our long history of working as one to benefit us all.”