Bomb-making guides are online, but getting them to work is not easy | Ewen MacAskill and Nick Hopkins

Security specialists agree it is easy to find step-by-step instructions on the internet on how to make a bomb in a kitchen using ingredients easily available on most high streets.

But there is no such agreement on how easy it is to build a bomb that will detonate at the time of the killer’s choosing.

The intelligence agencies are scouring records to see whether Salman Abedi looked on the internet for details on how to build a bomb. Information is openly available online in spite of regular police attempts, in cooperation with internet companies, to close them down.

The Guardian has seen a 30-slide guide about how to build a bomb posted on Facebook. Although it was removed by moderators, it had been on the site for some time - and reappeared again weeks later.

While sophisticated explosives such as Semtex are difficult to come by, would-be terrorists have long relied on more household materials such as certain fertilisers which can be ground down into a fine powder that is highly combustible or even certain hair products.

Al-Qaida first published details of how to build a bomb in a kitchen in 2010 and Isis has since followed suit, with step-by-step guides published online. The Al-Qaida, Isis and other plans are designed to be simple to follow.

But Raffaello Pantucci, a counter-terrorism expert at the Royal United Service Institute thinktank based in London, says it is as not as easy as it seems and some degree of expertise is required.

“You need to look back at the history of bomb attempts in Britain to see it is littered with people who failed,” Pantucci said. “To make a bomb you have to have confidence it will go off – and to go off when you want it to requires a certain degree of training and practice.”

He said that even those trained overseas in places such as Pakistan had seen their bombs fail to go off.

Until police have solid evidence that Abedi made the bomb himself, they have to keep looking in case there were associates who provided him with a bomb or showed him how to make it.

The government has tried to make it harder over the last few years to buy the household or gardening ingredients, including asking sellers to inform the police of anything suspicious. But beyond that there is little they can do.