I've only sailed out of Southampton once, WBTA November 2024, but after looking at all the various options I choose to hire a private transfer. Here is why.
1. Where you stay the night before doesn't matter. - The car comes to your location so if you want to save money on a hotel you can. We stayed in London for 3 days prior to sailing, but choose a hotel just outside the Downtown London and saved $100 or more a night.
2. You don't need to use multiple forms of transportation. - Taking the Train or a Bus is less expensive, but they both leave and arrive at specific stations. You may need to get a taxi on one or both ends of the trip to get to or from the station. The bus and train station are not near the port from what I found.
3. Minimal baggage handling. - Since the car comes to you, your not dragging your cases around to get to the bus or train and again from the bus or train to the cruise terminal. People also said there is minimal space for baggage on the trains and it is not near where you may be seated.
4. Flexible scheduling. - You can schedule a private transfer to pick you up at nearly any time. Most drivers are using GPS maps and can be alerted of slowdowns or delays. They MAY have the ability to alter their route easier than a bus to avoid some of them. Regardless of what method of transport you use, I highly recommend getting to the terminal early.
If there was a downside to using a private transfer it could be considered more expensive. But, I am not so sure of that. If you have to get a taxi or Uber to get to a station in London and another to get from the station to the port the cost gap narrows. In November it was only two of us, and the transfer was about $250, but the stress free morning being picked up at the door of the hotel and being dropped off at the terminal close to the baggage drop off was worth 3 times that. We had even opted to get a larger car to make sure we had room for all our luggage which likely was not necessary.
