This leaves the Government’s own public borrowing forecasts of £43bn this year, falling to £38bn in 2009-10, on extremely shaky ground.

Most economists believe Mr Darling will forecast much higher borrowing of between £60bn and £70bn for the current year.

Official figures have already shown net borrowing hitting a record £37.6bn between April and September - higher than the whole of the previous year.

The immediate £37bn cost of the banking bailing bailout could also push the Government’s net cash requirement this year above £100bn , according to Barclays Capital economist George Johns.

Lower expected growth could also meanwhile force the Treasury to cut revenue estimates in coming years – down £27bn in 2010-11 and £20bn in subsequent years, Mr Johns added.

The explosion in spending through the combination of banking rescues and an economic stimulus package is meanwhile set to push the Government’s issuance of bonds - bought by investors as an ultra safe home for the money - to more than £140bn, a record high representing around 10% of GDP.

Mr Darling is also likely to formally sound the death-knell for the once-vaunted fiscal rules which have been under review since the summer as net debt as a proportion of output soars above the Government’s 40% target in the years to come.

The golden rule - only borrowing to invest over the economic cycle rather than to fund current spending - is also set to be shattered by Mr Darling’s Keynesian spending splurge.

The mess this will leave the public finances in will have to be cleared up by whoever wins the next election as the keys to Number 11 Downing Street begin to resemble a poisoned chalice.

Investec chief economist Philip Shaw said: “The Government of the day is eventually going to have to restore fiscal rectitude via spending cuts, tax increases or a combination of both.”