Musket,
it is common knowledge that Labour policy was to enact the social chapter as enacted in The Maastrict Treaty. The concept of a minimum wage us contained within it.

It is not common knowledge.
It is bollocks.

Read this Institute For Government document.
You will find no mention of Maastricht, Social Contract or EU.

"A national minimum wage for the UK had been under debate in the Labour Party for decades.
However, in much of that time it was not only opposed by business, but also was a source of
controversy – or apathy – within the labour movement. The commitment to introduce a national
minimum wage featured in Labour's 1992 manifesto, but was a source of vulnerability rather than a
winning policy. Yet, two decades later, the machinery for setting the minimum wage established in
the early years of the Labour government survived a change of government and came top of our
poll of political studies academics for best policy of the last 30 years. This case study looks at how
this policy turnaround was achieved. "

http://www.instituteforgovernment.org.uk/sites/default/files/the_mimimum_wage.pdf