The signal that sent out was appalling. The days when public sector workers got excellent pensions only in return for low pay are long gone; official figures show median earnings for those who work for the government are higher than in the private sector. Across the country firms have been closing down their final salary pension schemes, while the number of private sector employees working beyond normal retirement age has been growing sharply and is up by nearly 100,000 over the past year.

The private sector has been taking the strain and there is more to come. The Turner commission’s recommendations, endorsed by the government, will see the state pension age rise gradually to 68 and everybody automatically enrolled into a new national pension savings scheme. But the public sector has sailed blithely on, cossetted from these realities. The government is creating “a divisive two-tier pension system”, said John Sunderland, president of the CBI, in a letter to the prime minister. It was also leaving “a problem deferred, to be paid for by future generations who deserve action now to tackle the £700 billion of unfunded pension liabilities in the public sector”.

Mr Johnson’s deal did introduce new arrangements for public sector recruits who join from next year onwards. Their retirement age will be 65 and their pension arrangements less generous. But that only emphasised the unfairness. Why should the millions of existing workers be protected and allowed to retire early? As David Willetts, the shadow cabinet member, put it: “The Arctic ice cap is melting more rapidly than the government is reforming public sector pensions.”

Now, belatedly, ministers appear to have realised the scale of their error and want to unpick parts of last year’s deal. As we reveal today, Hilary Armstrong, the civil service minister, has written to the cabinet warning it of impending ructions over her plan to make civil servants meet part of the extra cost of their generous pensions. Under her plan, half the additional costs arising from greater longevity and other factors will be met out of deductions from civil service salaries.

Civil servants make negligible contributions to their pensions. The contribution of taxpayers, by contrast, ranges from 17.1% to 26.5% of salary and averages 19.4%. Mrs Armstrong says future costs should be split 50-50 between taxpayer and employee and that the taxpayer’s average contribution should never rise above 20%. She warns that the proposal will be “deeply unpopular” with civil servants and will be interpreted by them as reneging on the previous deal. But she urges her ministerial colleagues to stand firm (unlike last time) so that similar changes can be introduced across the public sector.

The problem is that her modest changes do not go far enough. The current civil service retirement at 60 is like a cuckoo in the nest, an insult to the millions of private sector workers paying for generous government pensions out of their taxes. If ministers are prepared to risk strikes over Mrs Armstrong’s minor changes, they should be prepared to take on the unions on this fundamental point. It is not just about pensions; it is about Mr Blair’s willingness to force through public sector change in the final stretch of his prime ministership. On this, as in other aspects of public sector reform under his government, we fully expect to be disappointed.