Leading article: A murky affair that calls for a tougher British response

When Mahmoud al-Mabhouh was found dead in his room at a Dubai hotel on 20 January, few doubted that he had been assassinated. A military commander with the Palestinian group Hamas, he had escaped attempts on his life in the past. As for who had done it, there seemed two clear possibilities: either Israel's security service, Mossad, or a hostile grouping from among the fractious Palestinians. Either would have a motive, but the safer money seemed to be on Mossad.

Such a blatant political killing in the deceptive safety of Dubai should have been loudly condemned as an international outrage in its own right. But with the culprits long gone and the deed presumed to belong to the shadowy world of secret agents, it was soon eclipsed in the news cycle. And it would have remained so had not the UAE authorities released CCTV footage of the presumed death squad, along with details of the passports they had used, in an appeal for international help to solve the murder.

An already murky story had suddenly become a lot murkier. Not only that, but there was a distinct British and European Union angle. All 11 passports made public were from EU countries, and no fewer than six were British. Yesterday, it was disclosed that there were at least another seven members of the team, including two with Palestinian papers, and that Mr Mabhouh may have been lured to Dubai with the inducement of an Iranian arms deal.

The story turned murkier still when those Britons identified by their passports turned out to be resident in Israel, categorically denied ever visiting the UAE, and professed themselves horrified at what appeared to be the fraudulent use of their passport details. The sordid killing in Dubai now seemed to have not only a strong link to Israel but implications that went beyond Middle Eastern politics. Either a slew of Britons had been recruited to a regional hit squad, or – more likely – someone was using British identities for their own nefarious ends.

The signs now seemed to point even less ambiguously to Mossad, which had tried a similar trick with Canadian passports in 1997 in a (failed) attempt to kill another Hamas leader in Jordan. So what was the British government's response to the fact that someone had fraudulently reproduced British passports, and that this someone was quite possibly the security service of a friendly country?

Well, the Prime Minister called for a "full investigation" into how pseudo-British passports were allegedly used by Mr Mabhouh's killers – which sounded all very civilised and not terribly urgent. And had the Foreign Office made any representations to Israel? No it had not. Nor, it initially said, were there plans to do so – though the ambassador is now being called in today. Even accepting that suspects are innocent until proved guilty, this looks like extraordinarily supine behaviour in a situation where, in essence, the good name of our country has been impugned.

By making public some of the – impressive – evidence it has collected, the UAE seems to be saying that it wants to end the Gulf's growing reputation as a soft touch for other people's assassins. By showing the sophistication of its record-keeping, the UAE may hope to discourage others. But if political murder is now unacceptable to Dubai, how much more unacceptable should it be to the British government? Those false passports call for a much more muscular response than has so far been forthcoming.