I did not do my ATPL distance learning, but went full time course. Used to get up 05.00 in the morning, self study until 08.00, than go to class for 6 hours, back self study for 2 - 4 hours! Did the ATPL's in under 6 months, running a business with wife and newborn baby around us!
One tip I would give you, is that you can split the exams up more than Bristol offers you. In theory, you need to complete all 14 exams within 6 sittings! Bristol normally make 2 sittings, which I think can be a bit tough with your situation.
Do the course, but pace the exams, spread them over 3 - 4 sittings. These have to be done within 18 months from the first exam.
Now a tip to give yourself some more time, for when you need to complete your CPL/IR, save one exam until the end, example one of the COM exams, dead easy exam, done in 5 minutes! Complete all your 13 exams before, save this one until the end, just make it is done before the 18 month period runs out!
This way you, the countdown of 36 months for your IR/CPL does not start until you have completed your last ATPL exam, and I suggest the COM exam, because it is so easy, not much effort is required to pass it!
This gives your 36 months to complete your CPL/IR, and also gives you more time to hour build, specially in the UK with crap weather, you might need more time than you expect.
It will take a toll on you relationships/friends etc., you will have to make sacrifices, it is not difficult, it is just a lot of material to get trough, as some of it is quite essential for later, when you go to apply for a job!
I would say time-wise, expect at least to spend 4 hours a day, 6 days a week + revising question bank, as soon as you get midway into a subject.