I lost my 3-year-old grandson in the London tube. It was the longest 10 minutes of my life.

• I was visiting London with my daughter and her 3-year-old son Archie.
• In a second, Archie got on a subway train while my daughter and I were left standing on the platform.
• The next train was coming in seven minutes, and we panicked.

London is a fantastic city with history, parks, good food and drink with an excellent transport system. I was there for the day with Chantelle, my daughter, and Archie, my 3-year-old grandson. The unseasonal October sunshine made our walk around Hyde Park very enjoyable.

Heading to London Bridge for lunch, we turned into the nearest station, went through the barriers, and entered the depths.

The rush of air announced the tube arriving, Chantelle and Archie were just in front of me as we hurried down the stairs in Notting Hill Gate. Turning onto the platform it was already there, doors open. The midday throng meant we wouldn't get this one; I was already hanging back, waiting for the next one as the doors closed.

Through the commuter and engine noise, I heard my daughter scream. The tube started moving, and I saw her walking alongside, gesturing with her hands. Struggling through the crowd, I saw Archie on the train. There was no staff to be seen, no emergency phone on the platform, and no phone signal that deep underground. The white body of the carriage disappeared into the tunnel, and for a second, there was silence.

We hoped he'd get off the next station

Running the few yards to my daughter, I looked at the information board above her head. The next train would be in seven minutes.

Those seven minutes were the longest 97 years of my life.

"We'll get the next one. If you want, I'll run upstairs and try to find someone to get help?" Even as I was talking, she was shaking her head.

She said there was no point. By the time I'd get there and call someone for help, the next train would have departed. She said she had shown him how to get off the train and that he'd be waiting at the next station. She stopped for a second, then said, "I hope."

She seemed remarkably calm.

The thoughts that ran through my head at that moment weren't wonderful if I'm honest. Deep down, I know people are decent, and a small child alone will almost always be looked after.

Yet although the negative thoughts were strong for both of us, externally, my daughter was strength personified.

We got on a train

Unable to do anything positive except reassure each other that all would be well, we paced the platform, telling each other he was already off the train, neither of us knowing if this was the case. A train came through without stopping. My worst fear was this one stopping at the next station and Archie panicking when we didn't get off.

An eternity later, we jumped on a train and took the one-minute journey to Holborn station on different carriages to give us a wider search area.

As we pulled in, I frantically scanned up and down, looking for a tiny boy amongst a sea of adults. I ran onto the platform, pushing through those waiting, and less than 10 seconds later, I heard, "Dad."

My daughter was about 50 yards away, Archie in her arms, a group of about 10 glamorous women, and many tears. When I arrived, the ladies explained they were going to a show but had seen Chantelle pointing to Archie to get off at the next stop and did what anybody would have done.

The tears flowed for several minutes.

We offered to take the ladies upstairs and buy them all a drink, but they wouldn't hear of it, saying we'd have done the same had roles been reversed. We stayed with them, thanking them effusively until they got on the next train, before leaving and getting on a bus, Archie already fully recovered from his ordeal.

I went to London again recently with my now 13-year-old grandson, who is nearly as tall as me. It's been a long time since he held my hand, yet once on the tube platform, I felt him grab it and hold it tighter than any partner has ever done.