The Institute for Fiscal Studies said George Osborne may have to find another £11bn from tax rises or spending cuts if the economy does not pick up.

This is on top of £8bn of cuts already mooted in the Budget.

Mr Osborne will deliver his Autumn Statement on 5 December.

The IFS warned that the statement could bring "more fiscal pain".

A spokesperson for the Treasury said that the independent Office of Budget Responsibility (OBR) would make its economic forecast next week alongside the Autumn Statement.

The think tank's latest analysis takes account of "the now weaker outlook for the UK economy" and "the disappointing trend in tax revenues seen over the last seven months".

Figures last week showed the government borrowed more than expected in October with a fall in corporation tax receipts contributing to the rise.

The IFS said if borrowing continued at the same pace for the rest of the year, the government would miss its borrowing target by £13bn.

It sets out two scenarios for the economy:

• a relatively optimistic scenario, in which the increase in borrowing and the deterioration in growth prospects turn out to be temporary
• a relatively pessimistic scenario, in which the undershoot in tax receipts and the deterioration in growth prospects turn out to be permanent

It said that under the first scenario, "no further action above that already planned" would be needed for the chancellor to meet his fiscal mandate of balancing the budget by the end of a rolling five-year period, though he has already discussed the possibility of welfare cuts of £8bn over the two years from 2015-16 to 2016-17.

But under the second scenario, to meet that mandate would require extending the squeeze on public spending to 2017-18 and implementing a further £11bn of tax increases or welfare cuts, on top of the £8bn.

The Treasury spokesperson said: "Action taken by the government has cut the deficit by a quarter, whilst over a million new jobs have been created in the private sector, inflation is down, and the economy is healing.

"Britain still faces economic challenges at home and abroad but the government is taking the tough decisions needed to deal with our debts and equip our economy for the global race.

The IFS also said that Mr Osborne may have to abandon his other fiscal target - that debt should be falling as a share of GDP in 2015-16.