There had been reports of a power surge, but his superiors were concerned and wanted him to attend the scene with his explosives detection dog Ross.
“You always think – it’s just going to be another false alarm,” he said.
At the time, he was unaware that three bombs had been detonated on the London Underground, killing 39 people.
“I was in my van thinking I would cut across Tavistock Square and that’s when I saw the bus,” he added.
“The roof had been blown off, and there was some debris blowing around in the wind.”
Just moments earlier, a fourth suicide bomber had detonated a device on the top deck of a number 30 bus, killing a further 13 people.
“People were coming out of the bus, and they looked absolutely shellshocked and disorientated,” Mr Smith said.
“Clearly some people had some really severe injuries.
“I had to deal with what was in front of me. Doing nothing is never an option for a police officer.”
He cordoned off the area surrounding the blast site, and his dog started to search for any potential secondary devices that might have been planted.
A short while later, Mr Smith was called to Russell Square station, where survivors of a bomb that had exploded on the Piccadilly line were emerging.
“We certainly didn’t know that this was actually the train that had caused the initial power surge that was reported at King’s Cross,” he explained.
“It was only later in the day that you connect it all to a wider attack.”
The police officer remembers nurses from University College Hospital putting the wounded onto stretchers and trolleys to get them to the hospital.
“They were just people on the bus or the Tube going somewhere,” he added.
“They weren’t thinking about the horrors that the emergency services have to deal with.”
On Monday (July 7), London will mark 20 years since the bombings took place.
As the first major incident he ever responded to, Mr Smith said that the attacks were “more memorable” than most of the scenes he has attended.
“7/7 will be with everyone who was there, in different ways.
“I can’t say it was life-changing for me, and I don’t really talk about it.
“I don’t want to glorify what I did – it should be about the people who lost their lives.”
