What is your boss going to do when it comes to paying you your holiday accrued over the course of your maternity leave? Oh yes, I am sure he thinks you aren't entitled to holidays whilst on ML, but you are.
You were perfectly within your rights to ask to have your 10 days then start mat leave (how many weeks are you?) You will alos be entitled to 9 months SMP.
When you say you were paid sick pay, do you mean SSP? Your employer doesn't pay this, the government do and it is a statutory right
This is not a case of 'better to be paid next year than not at all', you are entitled, by law, to a certain amount of holidays per year and, within reason, you can have them when you like unless the firm closes for 2 weeks in the summer etc etc.
Do you have an HR department?
Please use the web sites linked here, print off what you are entitled to and post it too your boss recorded delivery so he cannot say he didn't receive it.
Don't let him get away with treating you like dirt - he doesn't tell you how long you have off, you tell him (as long as you dont take more than 12 months and are entitled to AML)
He really need to brush up on the legal side of things with regard to ML - be the one to tell him