On 4 August 2011, Mark Duggan was killed by police in Tottenham. Two days later, a peaceful protest escalated into a riot. The looting and arson that followed saw five people killed, dozens injured and businesses destroyed. This summer British troops protected Olympic venues. Last summer some wanted them brought in to restore order on London’s streets.

Yet remarkably, there may never be a public inquest into Mark Duggan’s death. The reason? Britain’s rules on the use of intercept evidence. For justice to prevail, the law must be changed.

Since 1194, coroners have held inquests to investigate deaths which are suspicious, violent or occur at the hands of the state. These inquests are public. They ensure not only that the facts are found, but also that justice is seen to be done. They satisfy our need to understand why the death happened and how future tragedies can be prevented.

As things stand, intercept evidence – records of tapped phone calls and intercepted emails – cannot be used in British courts or at public inquests. Therefore, because vital evidence regarding Duggan’s movements in the hours leading up to his death is intercept evidence, there can be no public inquest.

This is not the first time the British tradition of open justice has been hamstrung by these rules. Londoner Azelle Rodney died after being shot six times by Metropolitan Police officers in April 2005. Intercept evidence exists which could shed light on his death, but since this cannot be used in open court, no public inquest has ever been held.

The year after Azelle Rodney’s death, counter-terrorism police arrested 24 suspects in connection with a plot to bomb airliners by detonating explosives hidden in soft drink bottles. Yet even for this trial, intercept evidence obtained in Britain could not be used. In the end, prosecutors were able to show the jury some evidence but only because it came from the Yahoo server in the USA, not Britain.

The government has promised an inquiry, but that is not good enough. We need a full, public inquest led by a judge, with a jury deciding on the evidence. It is intolerable that in a civilised, democratic society the relatives of British citizens killed at the hands of the state can be denied a public inquest into their deaths. It is even more intolerable when that death led to days of chaos. We all have a right to an inquest.

The law is not only wrong – it is absurd. Intercept evidence is treated differently to other surveillance evidence. So if the police follow you, they can use what they see as evidence in court. But if they tap your mobile phone, they can’t even tell the court that they did it, let alone tell the court what they heard. On this issue, Britain stands alone. There is no law like this in the rest of Europe or the US. Indeed, the Americans would not have been able to jail mafia bosses like John Gotti without the use of crucial intercept evidence.  The Independent Police Complaints Commission agrees with us, as do the Metropolitan Police and politicians of all parties.

The communities affected by the riots are still tinder boxes. To avoid a repeat of that appalling violence, we need a public inquest which is open, fair and completely beyond suspicion. We need a renewed commitment to our country’s history of open justice. This is not the first time a death at the hands of the police has passed by without an inquest. If this law on intercept evidence is not changed, it will not be the last.

David Davis is Conservative MP for Haltemprice and Howden. David Lammy is Labour MP for Tottenham