I posted this picture on Twitter, saying it was the Barfleur sailing from Poole to Cherbourg. I received a correction via Twitter from Brittanny Ferries - it is actually the MV Cotentin, which is described on the Brittanny Ferries website as follows
"Brittany Ferries' freight-only vessel Cotentin provides a significant increase in capacity on the Poole to Cherbourg service during the week when not operating her weekly direct service to Santander. The weekend service 'opens' up a bypass service to Santander, enabling transporters to avoid the weekend driving ban in France.
The freighter provides space for 120 articulated vehicles year-round in 2200 lane metres. Accommodation for freight drivers is in 120 two-berth, en-suite cabins. The ship was constructed at a cost of some €80m in Finland and underlines Brittany Ferries' long-term commitment to its freight business."
Source - http://www.brittanyferriesfreight.co.uk/1430
It was great to receive the correction from Brittanny Ferries, and also to receive a compliment on the photo I posted, which incidentally was taken from Poole Quay looking towards Sandbanks.