The issue was I followed a recommendation to remove runAllManagedModulesForAllRequests="true" from the modules section of my application's web.config, however this caused the relevant application events to cease firing (as the module wasn't registered).
See article here, and further info regarding this issue in the comments. http://www.britishdeveloper.co.uk/2010/06/dont-use-modules-runallmanagedmodulesfo.html
Replacing the runAllManagedModulesForAllRequests="true" attribute has now resolved the issue, however I'm attempting to install the MS provided hotfix which is mentioned to remove reliance on this and/or manually registered modules.