BT's line rental is £17.99 per month. If you pay for 12 months in advance you get 10% off, bringing it down to the equivalent of £16.19 per month. Most people can't get reductions on those charges.
However if your brother receives certain state benefits he can get his line rental down to £15.30 per quarter (which is very close to the figure quoted in your post) by using BT Basic:
http://www.bt.com/includingyou/other-products-services-bt-basic.html
If he then wants to add a
limited broadband service he can pay £4.85 per month for it (while still receiving the discounted line rental):
http://www.bt.com/includingyou/bt-basic-broadband.html
However if he wants a 'full' broadband service he'll have to pay the regular line rental (plus, of course, the cost of the broadband access).