As WMcF states, this man was exonerated by Pakistan's civil justice system. In Pakistan, a person is usually tried by either a civil court or by an Islamic one, and the verdict of the relevant court is regarded as final. So it was extremely unusual that he should be brought before an Islamic court after being cleared by the civil justice system.
There was never any doubt that the gun which fired the fatal shot was owned by the taxi driver. The accused person's defence was that the taxi driver had tried to sexually assault him at gunpoint and that the gun had gone off in the struggle which followed. Trying to prove, or disprove, anything relating to sexual misconduct, before an Islamic court is notoriously difficult. For example a woman who claims she was raped must produce 4 male witnesses (all of whom must not be related to her) to support her case. Otherwise she may be charged with adultery.
It is right that the British government, and the British people, should respect the verdicts of foreign courts when those courts have systems of justice which comply with international standards. Regrettably, Pakistan's Islamic courts fall well short of those standards.
I should make it clear that I'm not particularly 'anti-Islam' (although, as a 'campaigning atheist', I'm opposed to all religions). I'm simply 'pro-justice'.
Chris