A former detective for the Metropolitan Police has claimed the blast at Parsons Green station was a "catastrophic failure" on behalf of the perpetrators.
Police have now confirmed the explosion at Parsons Green station on Friday morning is being treated as a terrorist incident, and the incident was caused by an improvised explosive device.
Pictures on social media appear to show the cause of the blast - a white cannister of some sort - and while there are injuries, no fatalities or deaths have resulted.
Peter Bleksley, an author and consultant, said "we should be grateful" the device failed to wreak "the complete horror" it might have been intended for.
He told Julia Hartley-Brewer: "Clearly if it’s declared a terror incident, then this has been identified as a device designed, made, constructed to cause death and mayhem.
"Let’s be exceedingly grateful no deaths have been caused, and while injuries have been done - and my thoughts go out to those people - I strongly suspect the situation could have been a lot worse.
"We’ll regard it as a catastrophic failure on their behalf to wreak the havoc they wanted to.
"Now the wheels will be cranking in motion of that mighty tool, the anti-terror capability of the police and security services.
"At some stage in the not-too-distant future, those responsible for this will be identified, they will be known to us, and arrests will follow."