A senior Tory predicted to me in opposition that austerity would usher in a new era of decentralisation in government.

New Labour, he said, couldn’t resist micromanaging public services; they had to show results from a spending spree.

By contrast ministers tasked with slashing budgets would be desperate to pass down responsibility for the worst decisions. This is the kind of power politicians are keen to give away.

He was right. The coalition have embraced the agenda of localism with some gusto. Now heartwrenching case of Riven Vincent has come along to test David Cameron’s resolve.

Here’s a key part of her statement, explaining why she felt it necessary to consider putting her disabled daughter into care because of a lack of support.

Carers across the country are struggling the same way. It’s not a new thing. It’s been going on for years and no one government is to blame. But I had hoped that after David Cameron came to visit me earlier this year following our exchange on Mumsnet, he would have done more to protect families like ours.

The money the government has allocated for short breaks and respite care – eight hundred million over four years – is not enough and worse still it’s not going to be ring-fenced. So there’s nothing to stop cash-strapped local authorities from using the money elsewhere.

This must be an excruciating case for Cameron personally. But it is more important than that. The Vincent family challenges a central theme of the spending review. It shows the limits of passing responsibility — and the dangers of what Nick Boles celebrated as the constructive “chaos” being unleashed in public services.

The immediate temptation will be for Cameron to say that respite care will from now on be ringfenced, to ensure that all eligible families are given a basic level of support.

But it will trigger a wave of compelling pleas to intervene from those suffering from worse services. If Downing Street give ground on this case, it will leave them defending a much weaker position in months to come.

What is the current defence? Well the Early Intervention Grant (which covers respite care) has been cut by a total of 11 per cent. Downing Street point out that a rising amount has theoretically been allocated for respite care. But it is ultimately it is for councils to decide, now the ringfence has been removed. Support for the Vincent family will compete with other good causes paid for through that grant, from vulnerable children and youth offending centres to funding for Sure Start.

Just think of the other horrible decisions that have been passed to councils. There is a 28 per cent formula grant, they’ll decide how to pay for £1bn of EU fines, and pick who will feel the pain from a cut in council tax benefit — the list goes on.

The Vincent case is a moving personal story with very high political stakes.

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