| Competition: | National Development League |
| Domesticcup1: | Champions |
| Domesticcup1 Winners: | Mildenhall Fen Tigers |
| Domesticcup2: | Knockout Cup |
| Domesticcup2 Winners: | not held |
| Domesticcup3: | Pairs |
| Domesticcup3 Winners: | not held |
| Domesticcup4: | Fours |
| Domesticcup4 Winners: | not held |
| Highest Average: | Dan Gilkes |
| League Above: | SGB Premiership 2021 SGB Championship 2021 |
| Prevseason: | 2019 |
| Nextseason: | 2022 |
The National Development League 2021 is the third tier/division of British speedway for the 2021 season.[1]
Due to pressures caused by the COVID-19 pandemic it was decided that the league would be decided by the final table standings only, with no playoffs being held. For the same reason no Knockout Cup would be held.[2]
There were significant changes from the previous 2019 National Development League speedway season. Plymouth Gladiators and Kent Kings moved up a division to the SGB Championship but the latter formed a junior side called the Kent Royals to compete in the development league. The Cradley Heathens had withdrawn after the 2019 season[3] and the Isle of Wight Warriors withdrew from the league in early 2021.[4] Stoke Potters lost their stadium and were unable to compete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. This was followed on 26 August by the Eastbourne Seagulls after parent club, the Eastbourne Eagles withdrew from the league because of financial problems. Their results were expunged.[5] Mildenhall Fen Tigers won their fourth Division 3 title since 2003.[6] [7]
| Pos | Team | P | W | D | L | 4W | 3W | D | 1L | L | F | A | Pts | |
| 1 | 10 | 4 | 0 | 1 | 2 | 1 | 1 | 1 | 0 | 488 | 408 | 26 | ||
| 2 | Berwick Bullets | 10 | 5 | 0 | 0 | 1 | 0 | 1 | 1 | 2 | 455 | 440 | 22 | |
| 3 | Belle Vue Colts | 10 | 3 | 0 | 2 | 0 | 1 | 0 | 2 | 2 | 433 | 464 | 14 | |
| 4 | Kent Royals | 9 | 1 | 0 | 3 | 1 | 1 | 1 | 1 | 1 | 409 | 396 | 13 | |
| 5 | Armadale Devils | 9 | 4 | 0 | 1 | 0 | 0 | 0 | 0 | 4 | 385 | 424 | 12 | |
| 6 | Leicester Lion Cubs | 10 | 2 | 3 | 0 | 0 | 0 | 0 | 2 | 3 | 429 | 467 | 11 | |
| Eastbourne Seagulls | withdrew 26 August, results expunged | |||||||||||||
| Newcastle Gems | withdrew, results expunged | |||||||||||||
The fixture between Kent and Armadale was not held following several postponements.[8]
The 2021 National Development League Knockout Cup would have been the 23rd edition of the Knockout Cup for tier three teams. However it was cancelled due to concerns over the Covid-19 pandemic.[2]