I regulary fly across the Bristol Channel and the Irish sea take a life jacket with you and a PLB and keep in contact with Cardiff or Swansea and you should be ok recently flew from Lydd to France you would n't have to worry about drowning there I think you would be run over by a container ship first !!!!!
With the Irish sea crossing unless your higher than about 3000 feet you will not be able to pick up Shannon or London Information.