UK maternity leave

Fatimah • Cooking baby #3 and #4⏳
Hi ladies
I'm a full time dental nurse living in the UK.
I think had the best bosses ever existed, a lovely Greek guys
They sold the practice now to a new owner. Who says she doesn't know how maternity works because the 30years she work she never had an employee thag got pregnant.
Being a first time mum im not sure how my maternity works.
I start my leave on January 2016
So I think I suppose to go back on September? Is that correct ?
And my old bosses use to pay the last month of the maternity pay as a month holiday pay. So is this something they done because they wanted to 
Or is it a regulation? And if is a regulation do I have to request it?