Quote Originally Posted by petom
The RAC was not a round of the Open Series in 1981 so it looks like either 1979 or 1980 was the last year in the Open Series.
The regulations for the 1979 Phonepower Welsh Rally list the Sedan Open Championship rounds as:

21/24 February Mintex International
13/17 April Benson & Hedges Circuit of Ireland
10/12 May Phonepower Welsh International
9/13 June Esso Lombard Scottish
9/12 August Burmah International
13/15 September Manx International
18/22 November Lombard RAC