The trees are silhouetted against a mottled crimson sunset, you can detect more than the occasional mosquito, and still the people keep arriving.

A veritable river of humanity, some 10 or 20 across, streams in from the tributaries of Park Lane and Marble Arch. My job, as I see it – and why I joined up – is to help make sure London does not let them down.

Since last Wednesday, I've been one of 12 "London ambassadors" working the evening shift in Hyde Park. We are all around London, in small groups or pairs, answering questions, handing out maps and timetables and Time Outs, and trying to be friendly and helpful. You can't miss us in our pink and purple tops – which is the whole idea of the uniform. It is quite a salutary experience for someone not in the service business – as journalists can rarely claim to be – to stand around and be nice to people for five hours. It turns out, though, that the smiling and helpful bits are many times easier than the wear and tear on the feet. We're allowed one 20-minute break, reporting on and off to our manager in the little kiosk, or pod, which functions like a mothership. But it can be a mistake to sit down; it makes getting up that bit harder.

What makes the nice and helpful part even less of an imposition, however, is that those who break away from that human river, looking uncertain or lost, or with a specific question that they sometimes struggle to formulate, in any language, are almost universally so polite back. I was five minutes into my first shift when an enormous Irishman came up to me very deliberately, and looked me straight in the eye. Any apprehension on my part was misplaced, as he shook my hand firmly and said he wanted to thank me, and all of us, for volunteering, and how wonderful we had all been, and would I please pass that on. So I'm passing it on.

Nor was he the only one. Every evening, the questions have been sprinkled with generous appreciation. Believe me, it's not just the athletes dissolving into tears. What is this country coming to?

Even when the answers are not what the questioner wants to hear – that it is a brisk 10-minute walk to the nearest Tube station that is not exit-only; that viewing the big screens is free, but beyond a security cordon; that they won't be allowed to take the lavish picnic they have just bought at a nearby supermarket through security – the response is universally philosophical.

The worst was having to warn people, arriving breathless from their trek from who knows where, that Usain Bolt's race was 20 minutes away and the queue for security was now an estimated 30 minutes, and that, alas, they weren't going to make it through in time. We suggested streets where they might find a pub with a television, but many just settled down with their sandwiches and Prosecco on the grass, and clustered around their mobile phones when the historic moment came.

I was set on volunteering from the start, on the grounds that London would not host so many people from so many places again in my lifetime, and as someone who has lived and worked abroad I wanted to help show off the city that is so often, and so unjustly, maligned.

There were few tangible rewards – it was stressed at the outset that this was not a fast track to obtaining tickets. We all received our uniforms, a travel card to pay our fares and £5 a day on a special Visa card for sustenance. That's it. But with the experience, and the memories, it was more than enough.