By Andy Silvester ONE of the country’s leading economic think-tanks has described estimates that Kwasi Kwarteng’s package of tax cuts in last week’s mini budget could cost £45bn as a “gross exaggeration.” The package has gone down badly with both markets and politicians, with the cost of UK borrowing spiking due to concerns over runaway government spending. However the Centre for Economics and Business Research said today that the package is more likely to sit around £25bn. The CEBR said “public borrowing may be less out of control than the markets think.” The group’s deputy chair said the Tre…