Iain Duncan Smith has a dramatic plan to boost home ownership.  According to James Forsyth in this week’s Spectator, he wants to broaden the right to buy for housing association tenants.  The money raised would be ploughed back into building new social housing.  The scheme could be announced in the Conservative Manifesto.

An obvious objection to the plan is that it would be unfair to tenants in the private rented sector, who would not have a similar opportunity – and anger them.  As Andrew Gimson has pointed out previously on this site, this was Margaret Thatcher’s original objection to Right to Buy – which turned out to be signature tune policy of her election-winning years.

It is tempting to view Right to Buy 2 (as we will call it) in exactly the same light.  Home ownership is extended.  Their former tenants come off housing benefit – so the state makes a saving.  New social homes are built.  Everyone wins: arguably, it is the ultimate ConHome Homes Jobs and Savings Policy.  Why doesn’t David Cameron screw his courage to the sticking place, and go for it?

Perhaps because there is an important difference between Right to Buy 1 and Right to Buy 2 (as we will call it). Under the former, the state sells off its own property.  Under the latter, it would be selling off someone else’s – namely, that of the Housing Associations.  Since they borrow to build social homes, and would no longer have a steady stream of income from housing benefit, it could leave them unable to pay back their debts.  Duncan Smith and Oliver Letwin, who reportedly is also keen on the plan, might answer that these would be covered from the money from sales, but the Treasury will be nervous about the sums.  No wonder George Osborne is apparently sceptical.

Another version of the plan is simply to give away council homes to their tenants if they have been in work for a year, take them off housing benefit, and charge them 35 per cent of the sales proceeds in tax if they sell their properties within three years.  But what they become unemployed, and want to claim housing benefit again (which, furthermore, isn’t simply paid to people who are out of work)?  And what if they need to move to get another job?  Wouldn’t it be unfair in such circumstances to tax them for doing so?

It may be that the numbers for both plans make sense when crunched, but such questions highlight another distinction between Right to Buy 1 and Right to Buy 2 – namely, that times have changed.  The structure of the jobs market is different (unions are smaller, the service sector is bigger, more women work in the labour market, and so on).  So is the housing market.  The average age at which one can buy a house has steadily increased as immigration has risen, household size has shrunk, London has grown even larger and prices have soared.  So where are the new homes envisaged by the Work and Pensions Secretary to be built?

This is why the housing section of the ConservativeHome Manifesto concentrated much of its fire on supply rather than demand – proposing community-led planning and new garden cities.  For only if more supply is married to home ownership can the cycle of pressure on councils to build, housebuilders spotting buy-to-let opportunities and poor quality housing springing up be ended.

The Work and Pensions Secretary is absolutely right to want poorer people to own their homes in larger numbers: it is part of the social justice vision that drives him.  But isn’t there a lesson here in his own Universal Credit plan?  It is being rolled out nationwide next Monday, the best part of five years since the Coalition took office.

The reason for the delay is that radical reform plus real time reporting plus new computer systems needed trial and testing.  So does Right to Buy 2, in either form – in combination with the movement of money out of Help to Buy, the building of more homes for sale by social landlords and experiments with new forms of ownership.  Let’s have a manifesto commitment – but to small steps, not a big bang.