Southampton is often the departure port for many no fly cruises and a no fly cruise has many advantages. You are not so restricted on luggage so you can cover all changes in climate and at the Port of Southampton you can park literally right next to where the ship docks, your bags will be taken from you as soon as you park and the next time you see them is in your cabin! We usually find when we leave the car we are enjoying all the fabulous facilities the ship has to offer within 30 minutes, so it certainly beats hanging around in Airport lounges for hours waiting for flights!
We highly recommend staying locally the night before your sailing to ensure a nice relaxing sailaway day rather than having to worry about getting stuck in traffic on the day. Infact there is nothing like getting up early on Sailaway day and watching your ship arriving at dawn knowing that you will be sailing out on it a few hours later!