According to the National Express East Anglia website if you take your bike from Colchester to London you do not need to book and it is free of charge. May be a goer, bear in mind the further away from Dunwich you get the easier it may be to get on a train, especially if it is on a different line to the Ipswich one, however I do not know if this is the case. Still debating with myself whether I should cycle there and back / there and part of the way back.
According to the National Express East Anglia website if you take your bike from Colchester to London you do not need to book and it is free of charge. May be a goer, bear in mind the further away from Dunwich you get the easier it may be to get on a train, especially if it is on a different line to the Ipswich one, however I do not know if this is the case. Still debating with myself whether I should cycle there and back / there and part of the way back.