Abstract. Photonic events with large missing energy have been observed in collisions at centre-of-mass energies of 130, 136 and 183 GeV collected in 1997 using the OPAL detector at LEP. Results are presented for event topologies with a single photon and missing transverse energy or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection. These results are compared with the expectations from the Standard Model process + photon(s). No evidence is observed for new physics contributions to these final states. Using the data at = 183 GeV, upper limits on and are derived for the case of stable and invisible Y. These limits apply to single and pair production of excited neutrinos ( ), to neutralino production ( ) and to supersymmetric models in which and is a light gravitino.