The latest Home Office figure for paying gun enthusiasts and dealers will be a blow to the Government, as the extra money is not included in the current budget.
The news came as the Government outlined its Firearms Amendment (No.2) Bill which proposes to outlaw the estimated 40,000 revolvers of .22 calibre and below which are excluded from a ban of higher calibre weapons introduced by the Tories.
The Bill gives MPs a free vote on the issue and with the huge Labour majority is sure to be passed.
First estimates put the cost of compensation at pounds 24m, but addition payments for accessories and ammunition increased the expected amount in November to between pounds 25m and pounds 50m.
But Home Office officials now believe the total cost for the additional 40,000 .22 guns and for payments to both dealers and private owners will be about pounds 150m. The gun lobby has argued that the amount will be far higher.
Of the pounds 150m, about pounds 12m will be used to pay compensation for the .22 guns and another pounds 19m for accessories of the smaller calibre weapons. The remaining money will be for the more powerful firearms.
Publishing the Bill, Alun Michael, a Home Office minister said: "In light of the Dunblane tragedy, it is clear that only the strictest firearms law can provide maximum safety to the public."Reuse content