The paper presents clear evidence of zonally symmetric planetary waves with very large amplitudes present in the UK Met Office zonal wind data of the Northern Hemisphere stratosphere in the winter of 2003--2004. The spectral analysis reveals that three prevailing periods of ~23, 17 and 11 days contribute to the observed zonally symmetric oscillations. These waves are extracted from the data and their amplitudes and phases are studied in detail depending on height and latitude. The wave amplitudes - particularly those of the 11- and the 17-day zonally symmetric waves - clearly indicate the presence of two latitudinal branches of amplifications centred at 50--600N and 20--300N. The phase analysis shows that these waves are vertically upward propagating waves and that the waves from the high-latitude and tropical branches are almost out of phase. A possible forcing mechanism is suggested. The zonally symmetric waves play an important role in coupling the dynamical regimes of the high- and low-latitude stratosphere particularly during the major stratwarm event in the Arctic winter of 2003--2004.