Much recent interest in the classic Casimir effect problem has urged us to treat this phenomenon carefully by giving special attention to the gauge problem, which has been almost entirely swept under the carpet in the past, and to seagull terms. By quantising in the so-called Coulomb gauge, where the dynamical degrees of freedom are apparent and the quantisation problem is unambiguous, the expression for the Casimir effect is derived by explicitly taking into account seagull terms. Although a physical quantity ought to be gauge independent a specific gauge, nevertheless, has to be chosen for its evaluation.