Answer:
There are many, important ones are (with largest settlement on the river included): the Severn (Bristol), Thames (London), Trent (Nottingham), Mersey (Liverpool), Medway (Chatham), Humber Estuary (Hull), Ouse (York), Aire (Leeds), Dee (Chester), Ribble (Preston), Tyne (Newcastle), Wear (Sunderland), Tees (Middlesborough), Test (Southampton), Clyde (Glasgow), Forth (Stirling) and Tay (Dundee).