Another update on the seatpost slipping issue - bumped into a friend last night who also has a swift. He has solved his seatpost slipping problem by getting his seatpost knurled. This makes the seatpost thicker as well as giving a more grippy surface. You don't have a lot of control over the thickness you add when knurling so you'd need to be careful the fit is loose enough before you knurl otherwise you it'll be too thick. Anyway it works for him.