Of all the measures in last week's budget that undermined the government's bare-faced claim to "fairness", the paring of unemployment benefit has to be the meanest cut of all. Jobseeker's allowance, to which unknowable crowds of people will be condemned if George Osborne's 25% public expenditure cuts are implemented, is already a pittance, impossible to live on.

People who have lost their jobs are shocked, when forced to sign on, to discover they are expected to eat, pay their bills, clothe themselves and get around – including for job interviews – on just £64.45 a week if they are over 25. For those under 25, weekly subsistence must be attained on just £51.85.

Osborne's announcement that the rate at which benefits rise will decrease, by linking them to the consumer price index (CPI) rather than, as currently, the retail prices index (RPI), was actually set out by the Treasury under the heading "Fairness".

On current figures, with the RPI at 5.1%, and the CPI at 3.4%, jobseeker's allowance was due to rise next year, to £67.87 a week for the over 25s, and a princely £53.77 for those under 25. Instead, the figures will be, respectively, £67.22 and £53.25. The loss is 65p a week for the over-25s, and 52p per week for the under 25s.

Those pennies all add up, as the government itself understands, calculating that this flick of the scythe across the benefit system will save it £1.17bn in 2011-12, and almost £6bn by 2014-15. Over a year, somebody unemployed over 25 will lose £33.80, while the under-25s will each be £27.04 worse off.

Before the election, I wrote that this poverty level of unemployment benefit, and the cruelty of a system that allows people to earn just £5 in part-time work before additional earnings reduce the benefit pound for pound, was a scandal no party was prepared to address. Donald Hirsch, author of a Joseph Rowntree Foundation report on the minimum needed for an acceptable standard of living – £13,900 last year, he found, way above jobseeker's allowance penury – said: "Everybody knows you cannot survive on that level of benefit."

I lamented that no party was prepared to raise unemployment benefit above the punitive, as governments, despite economic volatility and the cuts they themselves impose, continue to present jobless people as shirkers rather than desperately, temporarily, unfortunate. Yet still, nobody predicted that this Conservative-Liberal Democrat government would actually cut such meagre benefits in real terms.

The difference between the indices is that the RPI includes house prices, the CPI does not. The government's rationale for this nasty cut is that most unemployed people do not own their own house. So the change, according to the Treasury, "provides a fairer reflection of benefit claimants' experiences".

With this cut, and that almost sadistic misuse of the word "fair", the always ludicrous claim by Osborne and David Cameron, sons, both, of multimillionaires, that "we are all in this together", has irretrievably fallen away.