AMS,
Has as been stated above you need a PPL to start a ATPL Distance Learning Course.It would be wise to get a class one medical as well first.
You could save yourself £80 and get the class one straight away instead of getting a class two.
Distance learning is going to take about 12 mths to complete,a lot can happen in 12 mths.
I fly about once every 4 to 5 weeks whilst studying.Then once the exams are out the way I will hour build more often,but practise stuff that you will do for the CPL skills test.
Take an Instructor up every 10 to 15 hrs to make sure you are going in the right direction.Cheaper than getting to the end of a CPL and being told you need an extra **hrs at £**!!/hr.