The short certificate is issued free, and is still used to send in support of a child benefit application. It contains the name of the child and date/district of birth, nothing else.
A full certificate ( a copy of the register entry), which shows the details of the parents, cost £4 each at the time of registration (a statutory cost set by GRO) and most people get one, quite often two, but they don't have to.... it is optional.