My colleague Paul has come up with some very good additional readings on lobbying.
Dahan, N.M. (2009) "The four Ps of corporate political activity: a framework for environmental analysis and political action", in Journal of Public Affairs, 9 (2 ), pp. 111-123;
McGrath, C. (2006) "The ideal lobbyist: Personal characteristics of effective lobbyists", in Journal of Communication Management, 10 (1), pp. 67-79
McGrath, C. et al. (2010) "The evolving discipline of public affairs", in Journal of Public Affairs, 10 (4), pp. 335-352;
Industry Paper: (an oldie, but still a goodie - link supplied, and copy attached)
Parvin, P. (2007) Friend or Foe? Lobbying in British Democracy - a discussion paper, London: Hansard Society
[Accessed via http://www.hansardsociety.org.uk/blogs/downloads/archive/2007/09/24/friend-or-foe-lobbying-in-british-democracy-jan-2007.aspx on 20/11/2011]
Books:-
Strictly functional/nuts and bolts rather than theoretical, but in that respect, probably necessary and worth including. Has full section on the EU too.
Zetter, L. (2011) Lobbying: The Art of Political Persuasion (2nd ed), Petersfield: Harriman House