The Chancellor George Osborne and Douglas Alexander have asked the department's economists to calculate "in detail the figures that illustrate the benefits of the UK and the cost of independence". Economists spent months analysing forecasts, and spoke to independent bodies, the UK Government said.
The analysis will set out "in more detail than ever before the impact of having to absorb the higher spending and lower tax caused by declining oil revenues, an ageing population, the Scottish Government's uncosted policy pledges and the set-up costs of independence in a much smaller budget".
A spokesman for the Scottish Government said: "The fact is Scotland is one of the wealthiest countries per head in the world and is more than capable of being an economically successful independent country - the fiction is coming from Mr Alexander and his colleagues in the Tory-led No campaign."
More top news
Largely dry tomorrow with some sunshine in the south
The veteran singer showed even the greats have their off days when she had to stop halfway through and apologise to the audience.
So-called Islamic State fighters have re-entered the historic city of Palmyra in central Syria, activists say.