Is it similar to this sign?
It's not an impossible conclusion that the Red/Green lights in this situation are only for drivers - after all, a pedestrian would not need to open both gates and then come back across the road. And the signs imply that the green lights are only for those requiring to follow the instructions.
Of course the Red/Green lights and 'Phone if no light' instruction are also on pedestrian only crossings, so the lights do apply to all users, but it would be unreasonable to expect the average user of a crossing to know the national standards and conventions.
The strict answer remains the same - if you cannot contact the signaller you should find an alternative crossing. But it would not be unreasonable upon finding the lights out and the phones disconnected to look carefully both ways and then cross as quickly as is safe to do so, without pausing to take a photo.