London's Kings Cross station serves anyone arriving on trains from the north (even off-duty train drivers).

There would indeed be little point in supplying a coach to supply Tolpuddle from Waterloo - as of course you could get a train from there to Dorchester (or even Wool). However you would still have a bit of a problem -as public transport from there to Tolpuddle is not very frequent.

A shared taxi fare would not be too unreasonable however.