(27 May 2021, 7:48 am)big mac wrote I was thinking more from the point of view of the N prefix denoting that it is a "special" service, and that day passes etc won't be valid on them.  When a night bus ran previously on the 56, it was numbered N56 despite it having the same route as the day time service.

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It didn't have the same route as the daytime services. There's also been no announcement of fares, and judging by the Washington area routes, they look to be targeting factories. I think it might be regular fares, with the £1 single being valid 'till 3am.