Unit 3: The Changing UK System by Dr Alys Thomas Former Lecturer in Government at the School of Humanities and Social Sciences at the University of Glamorgan writes for BBC Parliament

Europe has been a divisive issue for both major parties

The UK has been described as an "awkward partner" in the European Union (EU).

It was not one of the six signatories of the Treaty of Rome in 1957 and eventually joined what was then called the EEC or Common Market in 1973.

UK governments have tended to place emphasis on the economic aspects of European integration whereas other countries have been equally concerned with political integration.

ALSO IN THIS SECTION: Unit 3 - The Changing UK System Do elections change anything? A need for constitutional reform? How united is the UK? Reading list

It was a Conservative Government under Margaret Thatcher which signed up to the Single European Act in 1986, aimed at creating a real single market.

However achieving this also required more common policies and more decisions and laws to be made at the European level.

In 1992 the Maastricht Treaty contained far reaching political and economic objectives including the creation of a single currency, a 'social chapter' guaranteeing a minimum standard for working conditions across the EU and the creation of a European Union with common citizenship.

Membership of the European Union is an intrinsic part of the political system in the UK. In some areas, such as agriculture, competition and employment, the UK government must pursue policies that fit into the parameters of EU law.

Critics of closer EU integration argue that membership of the EU undermines the sovereignty of the UK and that there is a democratic deficit because the EU institutions, such as the powerful, yet unelected, European Commission are seen as distant from ordinary people.

Supporters argue that the EU has helped to bring political stability to Europe and that in a global economy it allows the UK to compete with the internal EU market and as a bloc in world markets.

Divisions on Europe

Both main UK political parties have a history of division on the question of EU membership.

It was a Conservative Government under Edward Heath which took the UK in and splits in the succeeding Labour Government led the Prime Minister, Harold Wilson, to call a referendum on UK membership.

In the 1980s Labour changed its policy from one advocating withdrawal, and Euroscepticism hardened in the Conservative Party.

In the early 1990s the Major government faced backbench rebellions from Eurosceptic Conservative MPs who opposed the Maastricht Treaty, even though the UK had opted out of the single currency and the Social Chapter.

When Labour were elected in 1997 they signed up to the Social Chapter but the question of joining the single currency (the euro) remains a key political issue.

The Labour Government says that it is in favour of joining the euro in principle but the economic conditions need to be right. The Chancellor, Gordon Brown has set five economic tests. The decision will be subject to a referendum.

The EU has been a divisive issue in the Conservative Party since the late 1980s, triggering Mrs Thatcher's fall from power and casting a shadow over successive leadership elections.

In the 2001 General Election, the Conservatives made a commitment to 'save the pound' a key part of their campaign. However, some Conservatives are in favour of joining and were critical of this tactic.