24/11/2015 06:43 GMT | Updated 23/11/2016 05:12 GMT

When Is a London Flat Not a London Flat? When It's an Investment Opportunity in Kuwait

The other day a Green Party member in Greenwich sent me an advert she had found on Twitter for a housing development in her part of London. It's an attractive online brochure with enticing pictures of the Old Royal Naval College, Greenwich Park and other local landmarks including the Cutty Sark, the O2 and the Emirates Air Line cable car.

The text also stresses the excellent transport links to Central London. That might raise an eyebrow among long-suffering commuters on Southeastern Trains, but it's par for the course for an estate agent trying to emphasise what a great place this is to live.

Actually though, the advert isn't attempting to do this. It gushes that "the Royal Borough of Greenwich presents an exceptional investment opportunity" and notes that this development would give "tenants" a chic lifestyle within a prestigious development. In doing so it betrays some startling assumptions.

Even in the present climate of generous mortgage interest tax breaks for buy-to-let landlords and soaring private rents, new apartments are usually marketed on the understanding that at least some buyers will live there. But for this advertiser, owner-occupiers clearly don't enter into the picture. You can see why when you see where the firm itself - Cornerstone Global Investment Group - is based. The dialling code is 965, and the company is located on the 20th floor of a tower block in Kuwait City.

Don't get me wrong: I don't think foreign landlords buying property for investment are any worse than home-grown ones doing the same thing. Quite apart from the fact that this advert is in English not Arabic and therefore aimed primarily at Western expats in the Gulf, some landlords are fair and responsible, others less so, and nationality is no guide as to which they will be.

What matters for me is this labelling of flats as investment properties not homes, which speaks volumes about the warped priorities of the present building boom. There are cranes everywhere you look in London, but they are more about making our city's bricks and mortar a profitable repository for world capital than addressing the housing crisis.

As a Camden councillor, I know plenty of elected representatives - including a lot of Labour members - who agree that the housing crisis is shocking but insist we have to build these shiny new developments because they all come with a quota of affordable housing and that's the only way such properties will get built.

But I'm convinced that such developments, and the way they are marketed, are making the crisis worse. Treating housing as an investment commodity pushes the price of homes ever further out of the reach of people on ordinary incomes - never mind low ones - who instead have to pay ever higher rents to service the mortgage costs of the buyers.

I know about this because I'm a private renter myself who constantly feels one rent hike away from being pushed out of the city. And nothing exemplifies the problem better than this advert in an oil-rich Gulf state for "exceptional investment opportunities" in London.

Of course this kind of marketing isn't new. Reacting to a widespread feeling that it was wrong, Boris Johnson last year put in a place a voluntary agreement that developers would market homes in the UK before doing so abroad, or at the same time.

It's not clear whether the Greenwich developer has signed this so-called Mayoral Concordat, because the house-builder isn't named in any of the publicity materials. Even if it has, there is no suggestion it has breached the agreement - the same development is also being marketed in the UK via the estate agent Savills.

But this demonstrates the fundamental weakness of Boris' Concordat. In practice, as Green members of the London Assembly have helped reveal, the agreement allows developers to market first to a private group of British landlords, then abroad, before coming back openly to UK buyers.

What we need is a more robust commitment, and a binding one, that will ensure new homes are offered to Londoners first in a meaningful and accessible way. This might mean, whisper it softly, that the developers wouldn't achieve the best possible prices and that groups like Cornerstone ("dedicated to creating wealth for our clients") might find fewer easy pickings in London.

In other words, it would bring property prices down. Is that such a bad thing? There's a growing feeling among everyone I meet, from small business owners to providers of essential services and people like myself from Generation Rent, that that's precisely what we need.

Sian Berry is the Green Party candidate for Mayor of London, and heads the party's list of London-wide candidates for City Hall. She is the only party candidate for Mayor who rents rather than owns her home