[4] A double promotion from the Fourth to the Second Division hampered Cassells' chances at Vicarage Road and he made just 17 appearances before his departure in November 1980.
[3] Signed as a replacement for the injured Tony Mahoney, over the following 2+1⁄2 seasons he proved himself to be "a powerful-running frontman" and "a consistent, if unspectacular goalscorer".
[3] After rejecting a new contract, Cassells departed Griffin Park in August 1985 and finished his Bees career with 102 appearances and 28 goals.
[9] He had an excellent 1985–86 season, scoring a hat-trick on his debut and helping the club secure promotion to the Third Division with a third-place finish.
[5][10] He experienced more success in the following season, winning the 1987 Football League Trophy Final, despite missing a penalty in the deciding shootout.