The latest NOP poll has seen Labour double its lead over the Tories to six points in the past week.

The survey for Tuesday's Independent newspaper showed Labour on 38 per cent (up two points), the Tories on 32 per cent (down one) and the Liberal Democrats on 21 per cent (unchanged).

The party's lead had fallen in the previous two NOP surveys, from a high of 12 points in February.

More importantly for Tony Blair, some 67 per cent of Labour supporters say they are certain to vote, up three points on last week.

Predicting a lower turnout, other pollsters had even given the Conservatives on a small lead among those definitely set to participate.

But Labour voters are still less likely to turn out than Tory supporters - 78 per cent of whom are certain to vote (up one point from last week).

However, NOP takes account of this in its estimate of Labour's share of the vote.

With the electoral system slanted in Labour's favour, the findings point to another heavy majority for Tony Blair.

Tax

As the campaign shifts its focus to the main parties' tax and spending plans, NOP's findings have raised questions over Michael Howard's key policies.

Even among Conservative supporters, 58 per cent favoured spending any spare cash on public services, whereas only 30 per cent backed the Tory plan of £4bn tax cuts.

Overall, 65 per cent of the electorate favoured spending and 25 per cent tax reductions.

In contrast, the Liberal Democrat policy of a 50 per cent tax rate on incomes over £100,000 was popular.

Nearly three quarters of the public backed the idea, including 61 per cent of Conservative supporters and 80 per cent of Labour voters.

Constitution

Meanwhile, findings from MORI's poll of company finance directors were released in the FT on Tuesday.

The results showed nearly seven out of 10 oppose UK approval of the EU constitution.

However, over half of that figure are only "generally opposed" and could be persuaded to support the treaty in the promised referendum.