Hi Ian,
Good luck on your journey,hope you make it safe.To answer your question,Graham is right about the services.Generally you can quite easily park either in designated area or the truck park.The problem with the A1/M is knowing where the truck stops are.
You do not say what time you are setting off,but living just off junction16 ( near Daventry ) on the M1 I can tell you that the motorway gets extremely busy on Sunday afternoons.
Just 1 word of advice.If you decide to use the M1 don't stop until you clear Nottingham.You will then be beyond the heaviest of the traffic and broken the back of the journey (if you can last that long without stopping).The worst parts of the M1 for your journey are Northamptonshire,going past Leicester and likewise going past Nottingham.