The Conservatives say the 50p tax rate marked the death of New Labour
The Conservative lead over Labour has widened to 19%, an opinion poll carried out after the Budget suggests.
The ComRes poll, for The Independent, put the Tories on 45%, up five points and Labour down two points at 26%. The Lib Dems were down one point at 17%.
If people voted at a General Election along those lines it would give the Conservatives an 186 seat majority.
The Conservative lead is larger than those in pre-Budget polls, which put Labour support at about 30%.
An ICM poll for the Guardian on 20 April put Labour 10 points behind the Conservatives while a Populus poll for The Times on 3 April gave the Tories a 13 point advantage.
An IPSOS-Mori poll on 17 April also showed Labour 13 points behind the Conservatives.
The ComRes telephone poll of 1,003 British adults took place between 24 and 26 April, gave the Conservatives a wide lead over Labour when it came to confidence in their respective economic strategies.
But 79% of those asked said the opposition must give more details of its economic policies.
Andrew Hawkins, from ComRes, said recent polls suggested that support for Labour's handling of the financial crisis - which helped narrow the Conservative lead to 1% in December - had ebbed away.
In the Budget, last Wednesday, Chancellor Alistair Darling predicted that this year would be the worst the economy had had since 1945, borrowing would surge and also announced a new 50p tax on earnings over £150,000.
The Conservatives said the 50p tax rate marked the death knell of New Labour. Business Secretary Lord Mandelson denied that and urged voters to judge the decisions taken in the Budget in a year's time.