We went back from our home in France to see my folks in Southampton on 7th July for a week, took a bit of patience booking but the ferry was damn near empty going that way. Coming back from Portsmouth to Caen was a wholly different experience, huge queues and delayed departure. Mind you we were off the boat and through PP control in 7 mins which was nice! Maybe the french reg and LHD helps?!
Just booked a few days ago for a super quick trip back this coming Thursday as mum isn't well, but returning here on Sunday. Booking was a doddle to be honest.
Someone told me once that if you log in v early in the morning or around midnight you fly through the web booking process.