The Foreign Policy Centre and Community, the union, have jointly published an excellent brochure designed to contribute to the left's debate on Europe and the EU. I can heartily recommend it.

From the introduction:

"The insight that the peoples of the World are united by common
interests and a common humanity is obviously not a recent product
of the global era; it has been central to the socialist idea since its
birth. Yet the democratic left has often failed to translate its
internationalist values into the practical reality of a progressive World
order built on strong and effective institutions. The European Union
is certainly not perfect, but it is the most advanced and successful
international organisation that has ever been created. For all its
faults, it is living proof of humanity’s capacity set aside deep national
differences and order its affairs in common. That is too precious an
achievement to be squandered lightly or eve jeopardised by neglect.

"Europe must be more than a marketplace
for the free movement of goods, services, labour and capital. It must
be an instrument for regulating markets in the public interest and
restoring human values to the economic life of our continent and the
wider world. This is Europe’s rationale and its real achievement: not
simply the promotion of free trade, but the creation of a framework
that allows trade to be managed in accordance with rules and
institutions that are politically determined by elected governments.
In the real world this is something that even the largest European
countries can no longer hope to achieve on their own and must now
do by acting collectively. Real progress has already been made on
consumer standards, environmental protection, social rights and
much else. But Europe has the potential and the need to do a great
deal more simply because the greatest challenges, opportunities
and threats it faces today are transnational in scope.

"The purpose of this statement is therefore twofold: to restate the
democratic left case for the political and economic integration of
Europe and to set out a vision of how the European Union could be
reformed to make it a more effective instrument for social and
economic progress. No one imagines that this will be easy, but the
alternative of disillusionment followed by disintegration would be a
catastrophe for progressive politics and the security of nations."