A judicial review was heard at the High Court in February 2013 and judgment given on 25th April 2013 - R(HC) v Secretary of State for the Home Department  EWHC 982 (Admin) - Moses LJ and and Kenneth Parker J.
It is quite a lengthy and complex judgment so let's "cut to the chase."
The government had refused to extend to arrested 17 year olds the same protections offered to those under 17 who were arrested. The protections are set out in Code C to the Police and Criminal Evidence Act 1984. At the time, both the Police and Criminal Evidence Act 1984 and the Code permitted the police to treat a 17 year-old as an adult and, as an adult, he had no unqualified right to let his mother know what had happened, nor did his mother have a right to speak to him. Under PACE and the Code an inspector was permitted to delay such contact in light of his belief that it would interfere with the investigation.
The court stated at para 89:
" ..... it is inconsistent with the rights of the claimant and his mother, enshrined in Article 8, for the Secretary of State to treat 17 year-olds as adults when in detention. To do so disregards the definition of a child in the [United Nations Convention on the Rights of the Child], in all the other international instruments to which the Strasbourg Court and the Supreme Court have referred, and the preponderance of legislation affecting children and justice which include within their scope those who are under 18. The Secretary of State's failure to amend Code C is in breach of her obligation under the Human Rights Act 1998, and unlawful."
The topic is discussed in this article issued by Doughty Street Chambers - Law changed to protect 17 year olds in custody.
The government accepted the judgment and Code C was amended in October 2013 to require that an appropriate adult (e.g. a parent) be allowed access to a 17 year old held in custody. Access is on the same terms as it was previously for those under 17.
The Human Rights Act 1998 was used to make an important change which the government had appeared reluctant to bring about.
Please see this link and watch the video - Just for Kids - Everyday rights - when we need to protect our children
Some further anomalies remained in the law with regard to 17 year olds. The Criminal and Justice and Courts Act 2015 has provisions in it to address certain of these. For example, section 41
The effect of the Criminal Justice and Courts Act 2015 section 41 requires that if a 17 year old is to be given a youth caution or a youth conditional caution then an appropriate adult must normally be present.
A further matter concerned detention of 17 year olds in Police cells as opposed to being held in accommodation provided by local authorities - see UK Youth . This link mentions a number of suicides by 17 year olds who had been held in Police cells - (see pictures below). In 2014, the Criminal Justice and Courts Bill was amended and the outcome was section 42 of the Criminal Justice and Courts Act 2015. However, at the time of writing, it does not appear that section 42 has been brought into force.
PACE Code C - 2014 issue
End note 5th June 2015:
The government has announced that treating 17 year olds the same way as those under 17 when they are held by the Police will be addressed fully in a Policing and Criminal Justice Bill.
The Human Rights Act helps ordinary people every day. Let's fight to save it. #ActForTheAct http://t.co/uVKRXqG27e pic.twitter.com/lOLg08qkYP— Mary-Rachel McCabe (@MaryRachel_McC) May 27, 2015