Trust is a quality that is hard-won and easily lost.

For politicians seeking public support, it is vital. The claim that, post-independence, Scotland would automatically be a member of the EU under the same conditions as currently apply to the UK is such a key plank of the prospectus for independence that failure to ensure it was based on authoritative legal opinion is extraordinary.

The revelation that protracted Freedom of Information negotiations were to protect information that did not exist in the first place will re-affirm for many the view that no politician can be trusted. They also confirm the adage that it is not the lie but the cover-up that is most damaging.

The timing is also significant here. The disclosure follows the SNP conference vote to support an independent Scotland being a member of Nato. For many in the party, and others drawn to support independence because of the policy of nuclear disarmament, this U-turn is tantamount to betrayal.

It coincides with the disgust at allegations that Jimmy Savile abused youngsters on BBC premises and in NHS hospitals while those in authority turned blind eyes and the revelation that a senior BBC editor's account of why interviews exposing Savile as a paedophile had been shelved had been inaccurate.

The corporation's director-general was forced to admit to a committee of MPs this week that trust in the BBC had been shaken. The public service broadcaster, however, is merely the latest in a long, wearisome line of public institutions that have fallen severely short of expectation in the last few years. Greed, arrogance and self-protection have been the cause of failure of the banking system, and the scandal of ludicrous and, in some cases, excessive and dishonest expenses claimed by MPs.

Only yesterday, Sir Norman Bettison resigned as chief constable of West Yorkshire Police as a result of allegations he provided misleading information after the Hillsborough disaster in which 96 Liverpool fans died. But the real scandal was that not only did a large number of police officers in South Yorkshire seek to cover their own failings by alleging the fans were drunk and violent but that the families's complaints were dismissed for 23 years.

The public is heartily sick of being fobbed off. There is a hunger for truth and clarity that is supposed to be the result of every inquiry. But this week we have yet again seen prevarication and obfuscation from those in positions of power and responsibility.

The SNP achieved their majority at Holyrood on their record of a competent first term in government, with judgment suspended on the prospect of independence. Before that can be given, other questions must be answered, including whether an independent Scotland would have to apply for membership of the EU, the future of the nuclear bases and whether Scotland would be accepted into Nato with or without nuclear weapons.

Trust in politicians and in public institutions is at rock bottom for good reason. It can only be restored by honesty and transparency.