[2] There were significant changes from the previous 2019 National Development League speedway season.
The Cradley Heathens had withdrawn after the 2019 season[3] and the Isle of Wight Warriors withdrew from the league in early 2021.
[4] Stoke Potters lost their stadium and were unable to compete but there were three teams formed junior sides which joined the league, called the Armadale Devils (parent club Edinburgh Monarchs) the Berwick Bullets (parent club Berwick Bandits) and Eastbourne Seagulls (parent club Eastbourne Eagles).
Newcastle Gems had started the season but dropped out after in June after a couple of fixtures due to financial difficulties.
[5] Mildenhall Fen Tigers won their fourth Division 3 title since 2003.