There currently is one option to travel by night train from London (United Kingdom) to Penzance (United Kingdom), taking approximately 8 hours: Namely the Night Riviera Sleeper WB operated by Great Western Railway.
Great Western Railway (GWR) operates the Night Riviera, a sleeper train running six days a week between London Paddington and Penzance.
There are two options: airline-style seats at no extra charge, or cabins with a separate reservation. Cabin passengers enjoy a complimentary light breakfast on the train.
Sleeper cabins are available as either single or twin options. Each cabin has a sink with shelf and bin, UK power sockets, USB ports, a wardrobe, and under-bunk storage. The bottom berth transforms into a sofa during the day. Breakfast is served in your cabin.
Showers are available at Paddington, Penzance and Truro, but only for passengers who have booked cabins.
Cats, dogs and other domestic pets are welcome on board. Up to two pets can travel in your cabin without an additional pet fare, though a cleaning fee per cabin applies. Dogs must be kept on a suitable lead, and other pets must travel in a rigid carrier. Pets must remain on the cabin floor and are not permitted to sleep on beds. Only recognised assistance dogs are allowed in the on-board lounge, and pets should not be exercised in corridors or aisles.