The Conservative Party wants good schools to expand

They say this is because - with the state picking up the bill - parents would not actually be charged any fees.

Confusion arose because of remarks by different shadow ministers.

But it had been thought that the "passport" could be used for example for schools set up by parents and community groups, charging relatively low fees.

'Not one penny of subsidy'

The shadow health and education secretary, Tim Yeo, said earlier this week: "It is not the case that the pupil passport will only be available in the current state sector, merely that schools that receive the passport may not charge parents fees as well."

Any school that accepts children at the level of the passport is not a 'fee paying school' Tim Chatwin Conservative education adviser

Then education spokesman Tim Collins told MPs during the Budget debate on Thursday: "Not one penny of subsidy will be available for those who send their children to fee-paying schools."

A party education adviser, Tim Chatwin, said on Friday that Mr Collins meant that not one penny of subsidy would be available for parents to send their children to schools that charged above the level of the passport.

"In essence what he is saying is that any school that accepts children at the level of the passport is not a 'fee paying school' and any school that is above that level is a 'fee paying school' and does not qualify for the passport," he told BBC News Online.

A spokesperson said this meant that if the passport covered the fees, parents would not be paying any - so it would not be a fee-paying school.

Fee levels

The Conservatives have said the passport would be valued at about the cost of state education, currently £4,500 a year on average in England.

The Conservatives have yet to decide whether their passports would include capital funding.

But the Independent Schools Council Information Service said fees even at those levels would not cover many schools.

As a guide, fees for non-boarders range from about £4,500 to £9,600 a year in prep schools and £6,600 to £12,300 in senior schools.

Fees below £4,500 a year were actually charged in 48 prep schools and nine senior schools in 2003, according to its database.

Places issue

The Education Secretary, Charles Clarke, has sent the Tories a letter challenging them on their overall spending plans.

But in practice the passport scheme is not so much about money as places - primarily in state schools.

The key to it would be that pupils who wanted to take their child out of a school they did not like could get it into the school of their choice - which might well not have any places.

They say successful schools would be allowed to expand to meet the demand.

Asked whether any school that was full would be obliged to take pupils, however, a spokesperson said: "No."