 The City of Peterborough formed a parliamentary borough returning two Members in 1541 . The rest of the Soke of Peterborough was part of the Northamptonshire parliamentary county , except the area south of the River Nene in the historic county of Huntingdonshire and Thorney , which was considered part of Cambridgeshire . Until 1832 when the whole of the parish of Saint John the Baptist was encompassed , the boundary , as far as is known , excluded the villages of Longthorpe , Dogsthorpe and Newark with Eastfield . The Great Reform Act did not affect the borough , while the rural portion of the Soke was included in the northern division of Northamptonshire . New Fletton was transferred from Huntingdonshire in 1868 and in 1918 the parliamentary borough was abolished and replaced with a new division of the parliamentary county of Northampton with the Soke of Peterborough , including the whole of the Soke and neighbouring parts of the administrative county of Northamptonshire , extending down to and beyond Thrapston and Corby . This became a county constituency under the 1948 revisions , when the boundaries of the constituency were adjusted to correspond to those of the Soke and they remained much the same until 1970 . Peterborough became a county constituency in 1974 . 
