 He returned home following the Treaty of Berwick in June 1639 and by March 1640 had been appointed Recorder of Plympton St Maurice, Devon.In April 1640 Slanning was elected Member of Parliament for Plympton Erle, Devon, for the Short Parliament in what appears to be an unresolved double return.Slanning was Lieutenant-Colonel of a trained band of 157 men, two-thirds musketeers and the remainder pikemen.