While Boris Johnson and his cabinet scramble to deliver measures that will give Vladimir Putin pause for thought in his assault on Ukraine, another – lesser known – Briton is poised to have a potentially more significant impact.

Less than nine months into his tenure as the international criminal court (ICC) prosecutor, Karim Khan, a senior English barrister, announced this week that he had launched an investigation into the situation in Ukraine as there was “a reasonable basis” to believe that both alleged war crimes and crimes against humanity had been committed there.

There is no guarantee charges will be brought against Putin and his acolytes but some cling to the hope that the prospect of potentially having to stand trial in the future and of being arrested in countries signed up to the ICC may make some of them think again.

Prof Philippe Sands QC, who has known Khan since teaching him international law at King’s College London, said his former student had a tough job, but added: “All the signs are that he will have the capacity to be an independent, fearless and pragmatic prosecutor.

“He’s had an extremely impressive career as an advocate,” said Sands. “He’s got huge experience and brings to that job real knowledge and experience of what it means to prepare, conduct and litigate an international criminal trial.”

Reading law at King’s, Khan showed an early interest in international justice and human rights, something he has partly credited to his background of voluntary work with the Ahmadiyya Muslim community, a persecuted sect of Islam, of which he is a member. The community moved its headquarters to the UK in the 1980s after the Pakistani government passed a law forbidding Ahmadis from calling themselves Muslims and curbing their religious practices. Khan said his experience with them “helped me gravitate to this area [of human rights]”.

He was called to the bar in 1992 and cut his teeth with the Crown Prosecution Service (CPS). In his first published interview after becoming ICC prosecutor, he told Counsel magazine that seeing the horrors of the Balkans war on television made him aspire to work at the international criminal tribunal for former Yugoslavia, a goal he would eventually realise.

It proved the catalyst for him to advocate in a series of domestic and international criminal courts including the ICC itself, the international criminal tribunal for Rwanda, the extraordinary chambers in the courts of Cambodia and the special tribunal for Lebanon. His was not just a prosecutor, acting also as victims’ counsel and defence counsel. Last year, the Legal 500 described him as the “go-to lawyer” in international criminal law. In England, he was made a QC in 2012 and was appointed as a part-time judge in 2018.

Khan was sworn into office as ICC prosecutor in June last year, having been elected the previous February. He had not originally been on the shortlist and was added partly at the insistence of the Kenyan government.

Khan had acted as defence counsel for the Kenyan vice-president, William Ruto, when he was charged with crimes against humanity following post-election violence in 2007 that led to 1,200 people being killed. The charges were dropped in 2016 by the ICC after what was described as “troubling incidence of witness interference and intolerable political meddling”. One key witness was killed in December 2014.

Before the ICC election, Khan addressed this in an open letter detailing how he did all possible to prevent intimidation by ensuring the individual was put under witness protection and then seeking an inquiry.

His suitability for the ICC role was also questioned by some, given that he defended Charles Taylor, the former Liberian president who was convicted of war crimes at special court for Sierra Leone. But even those accused of the most heinous crimes have the right to be represented, while Khan’s experience both as a prosecutor and defence counsel is not without advantages.

Sands said there had never been any suggestion of inappropriate behaviour by his former student and the concerns about his election were more that he might be UK-centric – Khan’s predecessors were from the Gambia and Argentina respectively. However, Sands said Khan would do everything to avoid this and was well placed to do so given his personal background and vast international experience. He described Khan, who has studied and lectured on Islamic law and is a worldwide ambassador of the African Bar Association, as “a very modern British barrister”.

Having launched the investigation, Khan’s job now, with the help of a large team, will be to gather sufficient evidence to persuade judges to issue warrants of arrest or summonses to appear. Evidence-gathering generally involves a mission to the country concerned, as well as collecting video and photographic evidence.

With the ICC’s record on securing convictions a source of criticism, Sands said a key consideration for Khan would be who he chose to target.

“I think he’s going to have a policy decision of whether he just goes for low-hanging fruit, low-level perpetrators, or whether he goes higher up,” said Sands. “I think the ICC has aimed too high [in the past] and it needs to build a track record.”