In most cases you pay monthly instalments of around £24 per month for the first six months.
Then you start paying towards your next licence in the seventh month, with 12 monthly installments of less than £12 per month.
All your future licences will then be paid in this way.
I read this (from their website) to mean that you pay for your first years licence in six months (£144). Thereafter, you start paying for your next years licence 6 months before it's due, and finish paying for it 6 months after you get it. And so on year after year.
So you have paid 1.5 times the cost in the first year, but you've already bought half your next years licence.
Can't for the life of me see why though! Why not just £12 a month?