If you don’t think that mediation would help, you can contact a family lawyer straight away and ask them to apply for child contact through the courts. There are very many family lawyers who can help you to make an application for child contact to the courts.
Resolution (http://www.resolution.org.uk/) are the umbrella organisation for 5000 family lawyers, and their website is a good place to start your search.
Resolution also have an online advice centre and http://www.resolution.org.uk/landing-two-cols.asp?page_id=21
After you've made your application, the court will then appoint a specialist officer, called a CAFCASS officer, to assess the situation neutrally and prepare a report on what the circumstances are and recommendations for the future, based on what is best for your child. CAFCASS stands for Children and Family Court Advisory Support Service. You can find out more about the legal positions (and about what will happen if and when you apply to court) from the CAFCASS website