Normally I would keep on walking. Waitrose is over our budget and reserved for special treats. But last November I felt compelled to stop. I had gone to hospital earlier that day after my waters had broken, but I was sent home because I was only 1cm dilated. The contractions were every five to six minutes, so when my husband, Tim, suggested we get a bite to eat, I agreed.

My sister-in-law, Eunice, drove us to Canary Wharf in London, and in the restaurant the pains became so strong, I found it hard to eat. "Let's take a walk around the block," my mother-in-law suggested. "The baby's not coming yet."

I knew that my labour had stepped up a gear, but felt reassured by her words. "Maybe she's right," I thought as I waddled through Canary Wharf shopping centre. I went to the loo and, as I sat down, I felt the urge to push. I recognised the feeling from the birth of our son Ethan, now two, and knew the birth was imminent.

I went back out into the shopping centre. "Call your sister, the baby's coming," I shouted to Tim. Eunice had popped into Waitrose, where my auntie works, to buy us a few bits and her phone went straight to voicemail. I went to a corner outside the shop and leaned against the wall. The contractions were one after another and I was in agony. I spotted a maintenance man and asked for help. "What can I help you with?" he replied jovially.

"I think I'm having a baby," I said, and his face changed. In a matter of seconds, four security guards arrived, bringing a chair and some screens. "Do you want an ambulance?" one asked as they constructed a makeshift shelter.

Yes, I wanted an ambulance. I wanted somewhere quiet to give birth. There was no way I was doing it outside a supermarket. Even with the screens, I could see the feet of shoppers walking by.

While one security guard dialled 999, another took out his phone and Googled how to deliver a baby. I was determined he wasn't going to need that advice and sat with my knees clamped shut, even though I could feel the baby descending. Everyone around me was begging me to lie down. "Madam, you need to get into the birthing position," said a guard.

When I found out the ambulance was stuck in traffic and would be 20 minutes, I had to accept that I was going to deliver outside Waitrose. The manager arrived and instructed staff to bring out duvets, towels and blankets for me to lie on. Even in my haze of pain, I remember thinking that I wouldn't want to get blood on them because we couldn't afford to pay for them.

I'd grown accustomed to the male security guards, but it was a relief when a female one, Alexandria, took over. I warned her that as soon as I stood up, the baby would come out and she was incredible. She whipped off my boots, socks and leggings in an instant after I lowered myself to the ground.

By now, the urge to push was immense. All worries of where I was faded away. I simply focused on getting the baby out. With Tim propping me up from behind, I gave four huge pushes and the baby slid into Alexandria's hands. He immediately gave a cry and relief rushed through me. I didn't care where I was or who was looking, my baby was here and he was healthy. Alexandria passed him up to me and as I held him close I wondered why everyone around me was crying. I didn't feel tearful, just so grateful. I gazed down at my tiny son and he stared up at me, calm and quiet.

A nurse arrived and tied the umbilical cord with a shoelace – there had been an announcement on the PA asking for midwives, doctors or nurses in the shopping centre. The paramedics came soon after and wrapped the placenta in a Waitrose bag.

We were taken to hospital to have the baby checked out. Everything was fine and we were home the next day. We named him Matthew John, after John Lewis. They sent us flowers and vouchers, as well as giving us the blankets, which was a bonus.

I wouldn't recommend giving birth outside a supermarket, but it did turn out to be an unforgettable, joyous experience. I've been back to that shopping centre and felt a wave of emotion when I saw the corner where it all happened.

• As told to Emily Cunningham.

• This article was amended on 15 January 2013 to add the information that Daphne Bolus's auntie works at the supermarket.

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