The 15-year-old romped to victory in the intermediate 400m at Alexander Stadium, in Birmingham, recording a new personal best of 48.32sec in the final.
Richardson was always in control of the race. He led coming off the last bend and ran away from his rivals down the home straight, eventually winning by more than half a second.
“To win my first national title outdoors really means a lot to me,” the Costello School pupil said. “I felt a bit of pressure going into the race, but I knew that it was important I stayed relaxed. I knew I had a plan and I managed to execute it, with all of my sectors at exactly the right pace.
“I was relieved when I crossed the line and just really happy to have won the title. It was a strange feeling on the rostrum, because I had never been there before, but it was great.”
Richardson, the son of former Reading and Basingstoke footballer Steve, has flourished since moving up to the 400m at the start of the year.
“I just think that 400m really suits me,” he said. “At the start of the season, my aim was to run under 50 seconds, so to be running under 49 seconds fairly comfortably is a real surprise.”
Richardson’s victory means that he will make his international debut at the weekend, representing England Schools against runners from Scotland, Wales and Northern Ireland in Cardiff.
“I’m really excited to get the chance to run for England for the first time and hopefully I can get another win,” he said. “After that, my main aim for the rest of the season is the English Championships at the end of August.”
Richardson will be joined in the England team by The Clere pupil Holly Mills, who won the junior girls long jump at the English Schools Championships with a leap of 5.76m.
Another Basingstoke and Mid Hants athlete, Devon Brimecome, will also be in the team after picking up a silver medal in the intermediate girls 300m hurdles, finishing in 43.31sec, just 0.06sec behind the winner.
A total of 13 athletes from the Down Grange club travelled to Birmingham for the championships, with a further five finishing in the top eight.
Evie Wilcox (intermediate discus), Malachi Gair (junior high jump) and Hannah Haugvik (junior 80m hurdles) all finished fourth. Harry Richardson was fifth in the junior 800m, while Millie Cook was eighth in the junior shot.
In other athletics news, Andy Blow won the 100m hurdles at the Southern Senior Inter-Counties Championship at Mile End, while Basingstoke and Mid Hants’ Brendan O’Connor finished third in the under-20 1,500m at the Irish Championships.
Male and female teams from the Down Grange club travelled to Winchester for a Southern Counties Veterans League meeting. The men finished second, a result that leaves them third in the table, while the women sit second after winning their match.