1980–81 Isthmian League

Slough Town were champions, winning their first Isthmian League title.

Though, there was no promotion from the Isthmian League to the Alliance Premier League till 1985, at the end of the season two Premier Division clubs - Dagenham and Enfield were accepted to the APL.

Billericay Town finished second in Division One achieving the second promotion in a row.

Willesden folded at the end of the season.

The Premier Division consisted of 22 clubs, including 20 clubs from the previous season and two new clubs, promoted from Division One: There was no relegation from the division this season after Dagenham and Enfield joined the Alliance Premier League.