Ever since he took office in May 2010, British prime minister David Cameron has been determined that his government would not be dominated by Northern Ireland. Northern ministers would not have free or immediate access to 10 Downing Street. Matters that were the responsibility of the devolved administration in Belfast should be sorted out by it rather than being sent to London for final arbitration.

The logic of Cameron’s views was undeniable. In consequence, however, the British government no longer has the same level of relationships or finessed control enjoyed – or more often endured – by the last Labour government. However, Cameron moved quickly yesterday to cope with the crisis caused by Northern Ireland First Minister Peter Robinson’s threat to resign on foot of a London court decision not to prosecute John Downey for the 1982 Hyde Park bombing when it emerged that Downey was one of nearly 200 republicans who had been given letters telling them they did not face prosecution for any offences committed during the Troubles.

The decision of former prime minister Tony Blair to approve the letters was probably always likely to end up under the microscope of some judge, but no one could have expected that it would centre on the Hyde Park bombing, one of the Troubles’ worst atrocities in London.

However, the inquiry into the letters which Cameron offered yesterday is distinctly limited. Even though it will have power to look into "related matters", it will not look into the policy decision taken by Blair to offer the letters in the first place, a Downing Street spokesman told The Irish Times just an hour after Cameron made his announcement. This is not what Robinson was looking for on Wednesday evening when he was insisting that the letters would have to be rescinded.

Democratic Unionist MP Jeffrey Donaldson also made clear on Wednesday that the decision by the British Crown Prosecution Service (CPS), after talks with attorney general Dominic Grieve, not to appeal the Downey court judgment would have to be reviewed. Neither demand will be satisfied. The actions of the CPS are not reviewable by ministers, while Grieve and others have done everything possible to make it clear the letters will not be rescinded.

The focus on whether they could or could not be rescinded could potentially lead observers down blind alleys since the letters were not an amnesty but a declaration that an individual was not wanted for prosecution on a particular date.

Rescinding such a letter would not change the facts underlying it. However, it may prove far more serious in time that some people were told that they were wanted for prosecution. In effect, they were given an official warning to stay out of Britain and Northern Ireland or they would, if apprehended, be prosecuted for crimes they were suspected of carrying out during the Troubles.

Downey should not have been given a letter because he was a wanted man. There may be others on the list who were also wrongly given letters of comfort. In such cases, it would seem credible that those letters could be withdrawn.

Last night Robinson publicly drew comfort from the fact that people who received letters could not rely on them to save them from prosecution if new evidence came to the attention of the police or if old evidence existed. The letters never said otherwise. Individuals were told no warrants existed and that no police force had interest in them, but “if any other outstanding offence or offences came to light, or if any request for extradition were to be received, these would have to be dealt with in the usual way”.

The letters were clear – even if the letter to Downey was wrongly issued – that prosecutions were possible if new evidence was produced. In reality, the truth is that those responsible for piloting the peace process wanted the problem of the on-the-runs to go away.