Instructions: Answer the question from the given passage. Your answer should be directly extracted from the passage, and it should be a single entity, name, or number, not a sentence.
Input: Passage: Following the election of the UK Labour Party to government in 1997, the UK formally subscribed to the Agreement on Social Policy, which allowed it to be included with minor amendments as the Social Chapter of the 1997 Treaty of Amsterdam. The UK subsequently adopted the main legislation previously agreed under the Agreement on Social Policy, the 1994 Works Council Directive, which required workforce consultation in businesses, and the 1996 Parental Leave Directive. In the 10 years following the 1997 Treaty of Amsterdam and adoption of the Social Chapter the European Union has undertaken policy initiatives in various social policy areas, including labour and industry relations, equal opportunity, health and safety, public health, protection of children, the disabled and elderly, poverty, migrant workers, education, training and youth. Question: When did the UK formally subscribe to the Agreement on Social Policy?
Output:
1997