Detectives investigating the murder of Pc Keith Blakelock today said they were ''very confident'' of catching his killers as they began digging up a garden for vital evidence.

Commander Andy Baker, the Metropolitan Police's head of homicide, said ''first rate intelligence'' had led police to begin searching 16 Willan Road in Tottenham, north London, at 7am this morning.

Archaeologists were helping a team of specialist search officers, equipped with ground-penetrating radar, to scour the rear garden of the terraced house on the Broadwater Farm estate.

It is just a stone's throw from where Pc Blakelock, a 40-year-old father of three, was hacked to death by a mob armed with knives and machetes and Pc Richard Coombes was seriously injured during riots in October 1985.

The search is expected to last three or four days.

Police believe that evidence was buried there shortly after the murder.

Of the chances of this line of inquiry helping to bring the killers to justice, Mr Baker said: ''We are very confident - that's why we are doing it. ''It is not an issue about expense.

''This is about our ethos of relentless pursuit in any murder case.''

The current investigation started in October 2003 following a review and intelligence, which has helped lead to today's search, was ''firmed up'' over the last year or so.

Mr Baker said: ''We are searching for the truth. If we find out who the killers are we will put that before the Crown Prosecution Service and they will decide on that independently.''

He declined to discuss if the search was to try and recover the murder weapon or why it was so important to the case. He also declined to discuss any suspects.