It is a good summary. Not sure that ethically they should be putting this though....
"What you get will depend on what date your midwife
puts on your MAT B1 certificate when you are about 20 weeks pregnant, so you should discuss this with him/her before s/he fills it in."
They are right of course, but I'm not sure they should be seen to be encouraging people to try to influence their midwife in terms of what date is put as their expected due date...