The Tories are using their annual conference to cast themselves as the party of tax cuts - and the party that will benefit hard-working, ordinary families.

The shadow chancellor claimed to offer fully costed plans to make things easier for first-time buyers and families liable to pay inheritance tax. Soaring house prices since Labour came to power have had implications for the value for assets liable for death duties, and meant that more people are liable to pay stamp duty when buying a house.

The Conservatives reckon that raising the stamp duty threshold to £250,000 for first time buyers will benefit 200,000 people a year (adding up to one million over the course of a five-year parliament), at a cost of £400m. And raising the inheritance tax threshold - currently £300,000 - to £1m would cost £3.1bn a year.

To pay for these cuts, the party wants to bring in a flat-rate levy of £25,000 on non-domiciled residents - people who live in Britain but aren't classed as British residents, meaning they aren't liable for UK tax.

Do the promises add up?

First, let's look at the main money-making plan - the tax on non-domiciled residents. The Conservatives reckon that, at a cautious estimate, 150,000 residents would pay the levy, raising £3.5bn.

Cautious or not, clouds of uncertainty billow around this part of the equation. As Carl Emmerson, a deputy director of the independent Institute for Fiscal Studies points out, not only do we not know how many non-domiciles there are, it's also hard to say how many of them would choose to stay in the country if the Tories had their levy-levying way.

"They may all pay and there may turn out to be more here than they assume," said Emmerson. "Or they may prefer to go and pay tax on their foreign income."

Now let's look at the Conservatives' costed cuts. Raising the stamp duty threshold looks likely, over five years, to benefit the million people that the Tories claim.

But the maths behind those cashing in on the inheritance tax changes is far more sketchy. The Tories claim that Labour's inheritance tax net ensnares nearly 40 per cent of homes. This figure is based on the number of people who are currently estimated to be liable for the tax, rather than the number that are currently paying it - and it's a pretty big disparity.

In 2006, 18 per cent of properties in England were valued at more than the contemporary inheritance-tax threshold (£285,000). But in the same year only 6 per cent of estates were liable to inheritance tax, suggesting it's a tax hitting the richest section of the population, rather than the wide sting the Tories are trying to suggest.

Why such a difference? It could be that there are lots of people in their fifties and sixties who have a lot of wealth because of the value of their homes. However, this doesn't mean that they would necessarily have that much when they die - they may give it away, or spend it on long-term care, for example.

In their costed calculations, however, the Conservatives have used the current inheritance tax take - the £3.1bn paid by 6 per cent of households.

The verdict