The railway station shown is clearly not Witham despite what it says on the platform sign. The train is also of a rolling stock that had been withdrawn from regular service before 1985.
Jeremy and Julie are waiting at Witham railway station for Brett. A British Rail diesel multiple unit (DMU) arrives. But it's in its original 1950s green livery, a paint scheme which had entirely disappeared by @1970, if not earlier, a good fifteen years before the events depicted.