So, the cap is finally out of the bag. We now know what the Government’s own advisers have been telling prime minister, David Cameron, about the likely impact of the coalition’s ill-considered plans to introduce an overall benefits cap of £500 a week in 2013.

The proposed welfare reforms have clearly not been properly thought through and, if implemented, would result in unprecedented levels of child poverty and homelessness.

A leaked letter from communities secretary Eric Pickles’ office to Mr Cameron, and reported in The Observer newspaper, confirms what many of us have feared ever since the plans were first mooted – that they will have a devastating impact on the lives of thousands of children and the poorest families living in places like Haringey.

The note warns the prime minister that imposing a £500 weekly cap on universal credit could result in 20,000 families becoming homeless.

This is on top of the 20,000 households which the Government has already calculated to become homeless as a result of its cap on the housing allowance (LHA).

And there’s no point in the Government clinging on to the vain hope that the situation will be made easier for families if it disregards child benefit from the overall benefits cap. In London and the South East, this will still leave families with insufficient funds to live on after they have paid their rent.

A family with four children – living in a privately-rented home in Haringey [north London] – could receive housing benefit of £400 a week and, even if their child benefit of £60.50 is disregarded, the overall benefits cap will leave them with less than £20 a day to live on after they have paid their rent and council tax.

Even if the family was living in the council’s temporary accommodation, its members would still only be left with less than £24 a day to live on.

Leaving aside the substantial rent differentials between social rented housing and the private rented sector, it is clearly inequitable for the Government to apply the benefits cap without considering regional differences.

For example, in January this year, the weekly local housing allowance for a four-bedroom home was £375 in Tottenham, £300 in Reading, £242 in Milton Keynes, £184 in Birmingham, £173 in Leicester and £150 in Durham.

To put this into context, the same-sized family of four living in Durham would be left with £50 a day as opposed to just £24 in Haringey.

The capping of the housing allowance rates is already causing problems in London. Over the next 12 months, it is expected to result in an unprecedented increase in homelessness and ‘outward migration’ of low-income households from central London boroughs – where rents are a lot higher than the LHA caps – to outer London boroughs, such as Haringey, where the cost of private rented accommodation is lower.

Not only will this lead to untold misery and hardship for thousands of children and families across the capital, but will also cause havoc for authorities planning frontline services.

Outward migration will increase the demand for private rented housing in outer London – in turn, resulting in rent inflation together with increasing overcrowding and the use of unsafe, sub-standard and poorly-managed accommodation.

We are especially concerned about London boroughs’ use of out-of-borough temporary accommodation, as there is a very real risk that pressure on boroughs’ budgets will lead to a sharp rise in the number of such placements.

Having said that, it is very difficult to see how any large families living in temporary accommodation, or the private rented sector, will be able to remain in their accommodation if the Government proceeds with its plans to impose its benefits cap without regional variations.

As well as disrupting the schooling, healthcare and support networks of children and families, the use of out-of-borough accommodation will place considerable pressure on local social care, mental health and support services in those boroughs which are recipients of families. And I am particularly concerned about the safeguarding of vulnerable adults and children.

Perversely, the policy will also cause significant problems for those central London boroughs which see large numbers of children and families leave. I am aware of one such borough predicting it will have a 17% surplus of primary school places as a result of the Government’s changes to benefits.

These hasty, botched proposals, intended to grab headlines, will create a lose, lose, lose situation, and they certainly make the coalition government’s claims of creating a ‘fairer Britain’ ring hollow.

Claire Kober is leader of Haringey LBC