upbringing of child/sleeping habits

I have a question in relation to the general advice given by midwives and health vistors. in order to encourage a child to fall asleep on his own and not be scared or attention seeking the advice given is that if a child above the age of 1 years is waking frequently during the night and does not settle without a dummy or rocking etc then the child can be sleep trained by allowing it to 'cry it out' This means that slowly over a period of weeks the mother initially checks that the child is clean and not unwell then distances herself from the child for about 5 minuites then the next day 10 minutes etc and each day takes longer before going in to the child, leaving the child to cry in the bed and eventually fall asleep on his own. it is difficult to go into detail as the are many different approaches. the following quote is from the nhs website: "If your child cries, leave them for 5-10 minutes before going back in and settling them down again. Don’t pick them up or take them downstairs. If your child gets up, put them back to bed again." http://www.nhs.uk/Planners/birthtofive/Pages/Commonsleepproblems.aspx My question is that is this permissible? sorry for the lengthy question.