Two way switch controlling two lights

[Jock from the north]

Is this one of those complicated 2-way circuits where the 3 core passes thtrough the light fitting.... Maybe you've got the lights across the strappers. ?

Ha.had a whole school corridor like that when I was an apprentice ,was only changing type of fitting .nightmare .couldn't work out why there was so many cables at lights in connectors .had to get the big boss man out