When Bodie parts the curtains in Doyle's flat and sees Jill waiting in the courtyard, the closeup shot of his hand on the curtain shows he is wearing gloves, yet in the wide shots he is not wearing gloves.
The murder supposedly happened 7 years 5 months and 2 days ago. It starts in 1971 and then jumps to 1977 if you take away 7 years 5 months and 2 days away from 1977 it would go back before 1971.
In the flashback scenes of the murder of Fitch and Parker which took place during "a freak heatwave" during "the long hot summer of 1971", the trees are seen to be bare. Also, the summer of 1971 was actually unseasonably cold.
When Bodie and Doyle first arrive at the block of flats where Parker died, the marks on the ground indicating where the actors are to stand are clearly visible in the wide shot.
Bodie announcing the finding of the gun in the water states it is a 38 special 6 shot 3 empty chambers. But the chambers wouldn't be empty, 3 would have rounds in and 3 would have empty shell cases.
When Bodie and Doyle eventually locate Haydon's car in a second-hand car showroom, they discover that the radio is just a false front with knobs attached to a drawer where Haydon's gun was hidden. It is highly unlikely that the car would have been used by its other owners in the intervening six years without someone trying the radio and discovering that it was a dummy.
The flashback scenes happened in 1971 and present day events take place in 1977, according to the relevant on-screen captions. Also in dialogue the murder of Fitch and Parker is said to have taken place "six years ago". However Jill Haydon says that her father has been in prison for "seven years and five months" for the murders.