DIAS-STP-00-17 Gauge Invariance and Background Field Formalism in the Exact Renormalisation Group F. Freire, D.T. Litim and J.M. Pawlowski This preprint is not available for download on our website. To obtain copies of any of the preprints in the archives, please contact us and specify the preprint number(s), author(s), title(s) and number of copies wanted.