Runners have put their best foot forward for a pilot event on the road to a safe return of mass participation sport amid a "brilliant atmosphere".
The only running event in the Government's Events Research Programme began on Saturday morning at Kempton Park in Surrey.
Runners and spectators taking part in the Reunion 5K will help to provide scientific data on Covid-19 transmission levels, with both socially-distanced and non-socially-distanced runs being trialled.
Surrey County Council leader Tim Oliver said it had been "amazing" to take part.
© Provided by PA MediaRunners were taking part in a socially-distanced and a non-socially-distanced 5k (Yui Mok/PA)
In a video on Twitter, he said: "It was a brilliant atmosphere, everybody really enjoying themselves."
He added: "It's just a taster really of what normality might look like again, just amazing.
"So well done to Surrey for hosting it and well done to all the runners for participating."
All those in attendance had to provide evidence of a negative Covid-19 lateral flow test and were asked to take a PCR test both on Saturday and five days later.
Approximately 1,000 socially-distanced runners were to set off at regular intervals in the first group of races, watched by a socially-distanced crowd of spectators.
Some 1,000 runners were then set to take part in a non-socially distanced 5K, with onlookers also not required to keep apart.
Organiser Hugh Brasher, the event director of London Marathon Events, described the event as "such an important step towards the return of large mass participation events in towns and cities across the UK".
He said he had spotted that people have been cautious about entering an event which enables them to run in close proximity to each other for the first time in 15 months.
Speaking ahead of the event, he said: "With hindsight, this is entirely understandable when social distancing has been our way of life since lockdown began.
"Research is now showing that the risk of transmission of Covid-19 outdoors is extremely low and we all know how important exercise and these mass events are to mental and physical health, and to inspiring people to change their behaviour and adopt a healthier lifestyle."
Mr Brasher said he is hoping it will help see the return of all kinds of running events - ranging from park runs, the Great North Run or the London Marathon - to the sporting calendar.
Sports Minister Nigel Huddlestone said the Reunion 5k could help provide "essential data on the safe return of mass participation events".
© Provided by PA MediaHugh Brasher described the event as an 'important step' (Adam Davy/PA)
He added: "It's fantastic to see so many runners and spectators getting involved in this event which will feed into policy decisions ahead of step 4 of the road map and hopefully see things like the great London Marathon return with crowds."
However, Tom Williams, chief operating officer of Park Run, cast doubt on the return of that event if they can only hold some runs and not others.
He said some local authorities had said it "might take six months to get approval through a safety advisory group", with some saying local R numbers would need to be taken into account.
He told BBC Radio Five Live: "If we only open a small subset of our events, then the ones that did open would be overwhelmed with participants from the events that were closed.
"In England we have three million people registered to park run and on a normal Saturday prior to Covid we had about 200,000 people taking part.
"So, unless we get the very large majority of all of our events open at the same time, we won't be able to open any of them."