Nicola Sturgeon has been accused of undermining the SNP's new economic blueprint for independence after failing to answer "the simplest of questions" about its contents during a car-crash TV interview.

The First Minister repeatedly avoided answering how much the growth commission report said it would cost to set up a Scottish state, before finally admitting she had forgotten.

In another deeply embarrassing lapse, she also could not recall the blueprint's costing for a new social security system but insisted both numbers were "realistic.

Ms Sturgeon is usually an accomplished media performer and extremely well briefed, but opposition parties said the exchanges with Channel 4 News demonstrated a "lack of confidence" in the report.

The Tories said she was "unable to remember fantasy figures for set-up costs from a report she still insists is credible." Her interview came ahead of her keynote speech on Saturday to the SNP conference in Aberdeen.

The gathering is being staged against the backdrop of a Left-wing backlash against the growth commission report, which recommends severe spending restrictions and unofficially using the pound with no control over monetary policy.

Ms Sturgeon has been eager to establish the document's credibility by arguing it does not shy away from the hard facts of independence.