He joined Frank Clark's Nottingham Forest on loan in February 1996, and made his Premier League debut on 2 March, in a 3–1 win over Sheffield Wednesday at Hillsborough. He scored his first top-flight goal a fortnight later, in a 1–1 draw with Middlesbrough at the Riverside Stadium, though would only make one further appearance in 1995–96. Allen moved to the City Ground permanently in the summer for a £400,000 fee. He then played 23 Premiership games in 1996–97, and also scored against Ipswich Town in the FA Cup; Forest were relegated at the end of the season. He appeared in just one league game under new manager Dave Bassett in Forest's 1997–98 promotion campaign, though he appeared in both legs of the 10–1 demolition of Doncaster Rovers in the League Cup, finding himself on the scoresheet for the 8–0 triumph at Belle Vue.