Government reforms designed to restrict arrests for crimes of universal jurisdiction survived new challenges in the House of Lords last week. If the proposals emerge unscathed after a further debate this month, there will be less risk that politicians visiting Britain from countries such as the US, China and Israel will find themselves arrested by the police before being released almost immediately with the government’s apologies.

After I wrote here last year about the Labour government’s plans to stop private prosecutors obtaining arrest warrants in Britain for grave offences committed abroad, a reader complained that I should have declared an interest. Very well: I support the planned reforms.

I think it is right that politicians and others who previously served as defence ministers or military officers should be able to attend meetings in Britain without the risk of being detained on what Lord McNally, the justice minister, described last week as ‘very spurious grounds’. As the law now stands, anyone can secure an arrest even though the attorney general’s consent is required for a prosecution founded on universal jurisdiction.

Private prosecutions in such cases are unlikely to get as far as a court. But that is not the point, as McNally made clear. ‘The gain for those wanting to raise these issues is not in the trial or the verdict but in the publicity gained by getting the individual into the situation in the first place,’ he said.

McNally hinted that the government’s objective was to facilitate future talks in London between, for example, terrorist groups and the states that they had been attacking. The minister noted that successive governments were concerned that ‘the present weakness of our system could be exploited at a time when we would want to use all our influence’.

Clause 154 of the Police Reform and Social Responsibility Bill would require the director of public prosecutions (DPP) to agree before an arrest warrant could be issued to a private prosecutor in respect of piracy, war crimes, hostage-taking, hijacking or other grave crimes committed abroad.

The current DPP is Keir Starmer and, in January, he told MPs that he would issue guidelines explaining when he would give his consent. As with decisions to prosecute, sufficient evidence would be needed and the prosecution would have to be in the public interest. If an arrest decision had to be made within a few hours – presumably because a suspect was about to leave the country – the DPP would make do with what he calls the ‘threshold test’, consenting to the arrest if he was satisfied that enough evidence would become available within a reasonable period of time. Both of these tests are more demanding than the one normally used by a magistrate, which amounts to little more than asking whether the papers disclose an arguable case.

During the bill’s committee stage, peers debated an amendment moved by the Labour peer Lord Campbell-Savours. This would have watered down the government’s proposed restrictions: a magistrate would merely need to ‘take into account’ any advice given by the DPP on the likelihood of a future prosecution. The final decision on arrest would have been one for the court.

A broadly similar amendment was put down by the Liberal Democrat peer Lady Tonge. Both reflected the views of the joint parliamentary committee on human rights, which reported in May. Its members had not been persuaded that an arrest warrant should be issued ‘only where there is a real prospect of a viable prosecution’, in the minister’s words. Instead, the committee wanted to retain the current low threshold for arrest.

One person whom peers had been hoping to hear from last Thursday was Lord Macdonald of River Glaven QC, a former DPP. The Lib Dem peer had tabled an amendment that would have required his successor as DPP to consent to an arrest in cases where the evidence was incomplete, even if he thought the prosecution was not in the public interest.

Alas, Macdonald did not make it to the Lords last Thursday evening – nobody explained why – but his amendment was supported by a fellow Lib Dem backbencher, Lord Thomas of Gresford QC. Asked by Lord Goldsmith QC to explain why Macdonald had proposed that the public interest test should not apply in routine cases, Thomas admitted that this was not what was intended.

Peers cannot have been impressed, particularly when Lord Carlile QC pointed out that Macdonald’s amendment would have prevented prosecutors from using the most up-to-date prosecution guidelines. Carlile also dismissed the suggestion that a consent requirement would hold cases up: his wife is Alison Levitt QC, the DPP’s principal legal adviser, and she was used to taking decisions in the middle of the night.

But the most powerful speech of the evening was made by yet another QC, Lord Pannick. With economy and style, he laid bare his opponents’ arguments. The need to get a magistrate’s consent before the issue of a warrant was no safeguard for defendants because magistrates did not assess the evidence or apply the prosecutors’ code. There was no reason to doubt that the DPP would act independently of government. There was no reduction in Britain’s commitment to universal jurisdiction. The DPP would act quickly if required. Individuals could still bring private prosecutions. Finally, said Pannick, parliament should not tell the DPP how to exercise his discretion.

Pannick’s speech was so good that McNally, the minister, wondered if the cross-bench peer was after his job. I rather doubt it.