Some of the more notable past and present members of the Celtic League have been Plaid Cymru leaders Gwynfor Evans and J. E. Jones , Scottish National Party leaders Winnie Ewing , Robert McIntyre and Rob Gibson , leader of Sinn Féin Ruairí Ó Brádaigh , prominent Breton exiles Yann Fouéré and Alan Heusaff , the historian and writer Peter Berresford Ellis , writer Bernard Le Nail , and Manx language revivalist Brian Stowell .