IT started with a hardy group of 13, beginning their weekend with a five-kilometre jog around London’s Bushy Park.

Fourteen years on and the Parkrun phenomenon – a free, weekly timed run held up and down the UK and in countries from Russia to Malaysia and Australia to Swaziland – has reached an eye-watering milestone. It’s 5,000,000th runner.

I’m one of them – and I can’t imagine a weekend without a Parkrun.

For myself and my 11-year-old son, it’s become a staple part of our Saturday mornings (they all start at 9am).

If ever we have to miss one, we hate it.

And every time we do take part, our experience is entirely positive - satisfying, rewarding and uplifting. The most wonderful way to meet people and build fitness in a welcoming, encouraging atmosphere.

Our ‘home’ Parkrun is at Clacton – celebrating its 100th event this weekend - but we are also regulars at Harwich and others in the area include Colchester, Mersea Island, Maldon and Great Notley.

For those that don’t know, Parkrun is a national initiative with events taking place up and down the country.

All you do is register online – a quick and painless exercise – and then print out the sheet of barcodes that will be delivered to your inbox.

Bring one of the barcodes along and then, after completing the run, you are given a plastic chip.

Hand the two in together to one of the volunteers at the finish and your time will be recorded, emailed to you and published online later in the day.

Parkrun has been described as the biggest thing for athletics since the inception of the London Marathon in 1981.

It’s easy to see why.

While other well-intentioned, government-backed initiatives to get people active have come and gone, Parkrun is here to stay. It’s snowballed beyond belief and the number of registered runners will only grow.

In 2005, the average finish time was 22 minutes and 16 seconds.

Last year, having risen every year since, it dropped to 29m 6s.

However, organisers are delighted because it shows their event is all-inclusive and for everyone, not just seasoned athletes who regularly pound the streets for ‘fun’.

That would certainly be my experience, too.

You can be as competitive as you like.

Yes, club runners will jostle at the front of the start line and their competitive juices will be flowing as they race each other and the clock.

But the real inspirations are those at the back of the pack, having bravely taken the plunge to turn up and get fit, to lose weight or meet like-minded people.

Those runners can gauge their progress by checking their time, trimming seconds and celebrating the holy grail of a personal best (PB).

Generally speaking, it’s not a serious, super-competitive environment.

Children take part, people push buggies and wheelchairs and others have dogs on leads. Some even walk the route, rather than running.

The truth is that it doesn’t matter. Neither does age.

What matters is being part of something special – a heart-warming global success - and the satisfaction of having got some exercise with the whole day and weekend ahead.

Talking of special, high praise must go to the “high-vis army” – the tireless volunteers who don their fluorescent jackets and give up their time to make sure the runs go ahead.

Parkrun wouldn’t exist without them and both my son and I owe them a debt of gratitude. As do the other 5,000,000 Parkrunners.