My longcase clock (Charles Taylor, Kinross, Scotland - 1836) strikes correctly from 1 to 9, then strikes 1 for 10, 1 for 11 and then no strike for 12. Can anyone suggest where the fault might be, or was it a 'fix' to stop too many strikes at an inconvenient hour of the night?

Can you provide a picture of the movement, or at least describe the striking mechanism. Is it a rack strike count?

wow, that sounds like the same problem I am having with a small carriage clock (rack and snail). It strikes good at 1, but when it gets to 2, it chimes 1 and it will do it again at 3. Its regains its strike at 4...

I know this is not a longcase, but it sounds like we are having the same problem..

sorry about the photo being upside down (its right when I upload it )

In the case of your tall case clock, I would check the tension of the spring that pushes on the rack. Another thing to check would be the lift on the hook that counts off the hours to see if it is clearing the rack as it tries to fall away.