By who? Use Google if you need reassured. In the meantime I can supply these - I'm not sure how quickly you read, so I've put page numbers where only a part of the article / book is relevant. I have plenty of post 2001 if you like, but you appeared to need citations for my point about the Blair govt split on the EU. I've gone for my own preference as I wasn't sure if you preferred Harvard/Chicago style citations - Each university tends to have their own conventions on this tbh.
Meredith, Stephen C. "A Catalyst for Secession? European Divisions on the Parliamentary Right of the Labour Party 1962–72 and the Schism of British Social Democracy." Historical Research 85, no. 228 (2012): 329-51.
Crain, M., and K. Matheny. "Labor's Identity Crisis." California Law Review 89, no. 6 (2001): 1767-846.
Rothchild, Donald. "British Labour [party] and European Union." Social Research 23 (1956): 89-105.
Aughey, Arthur. Nationalism, Devolution, and the Challenge to the United Kingdom State. London ; Sterling, Va.: Pluto Press, 2001.
Bulmer, Simon. "New Labour, New European Policy? Blair, Brown and Utilitarian Supranationalism." Parliamentary Affairs 61, no. 4 (2008): 597-620.
Gaffney, John. Political Parties and the European Union. London ; New York: Routledge, 1996.
Heath, A. F., Jowell, Roger, and Curtice, John. The Rise of New Labour Party Policies and Voter Choices. Oxford: Oxford University Press, 2001.
Baimbridge, Mark., Burkitt, Brian, and Whyman, Philip. Implications of the Euro a Critical Perspective from the Left. London: Routledge, 2006.