Tony, It might be a good idea so as mistakes are not made, that you do read the whole of the thread and the appropriate dates on this matter of law. The fact that your car passed its MOT, is not unusual, but most MOT inspectors are aware of the law and can rightfully fail relevant cars.
Class 3,4,5 and 7 vehicles
For class 3,4,5 and 7 vehicles, the defect ‘Light source and lamp not compatible’ only applies to vehicles first used on or after 1 April 1986.
Should a vehicle be presented for an MOT test with conversions before 1 April 1986 they must not be failed with immediate effect.
Vehicles presented with converted halogen headlamp units first used on or after 1 April 1986 will continue to be failed.
Headlamps must comply with all other requirements of the test and headlamp aim.
The cars and passenger vehicles inspection manual will be updated shortly.
Regards and Best Wishes , John