Just read this:
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which was published in 2007 in relation to the 'indoor smoking ban'.
It says
The byelaws are from 2005
This, by implication, permits smoking where there is no such notice.
It is not really clear what is meant by "using existing railway bye-laws", but this could mean "stick up notices everywhere" or "change the bye-laws to effect such a ban".
It seems that the latter would be more logical - but it hasn't happened.
Any thoughts?