The recent work by Bevins et al in Journ.Arch Science clearly demonstrates that no sandstone from the Mill Bay/Milford Haven area is present at Stonehenge as prevoisly suggested by Atkinson amongst others.
Milford Haven as a shipping off point therefore is redundant.
Work over the last 14 years (especially the last 10) has shown that the northern slopes of the Preseli Hlls were the focus for bluestone collection hence a land route from the Preseli Hills to the river Severn in England now seems the most logical.
Work is currently focused on the exact provenance of the Altar Stone - and there is much panting of breath and crossed fingers.
Current Archaeoogy- a British Archy Magazine will carry a feature on this and other aspects in Sept/October.