Some of the most modern City Sightseeing open toppers back in 2005, aside from the latest Ayats deckers, were the Lothian operated Dennis Tridents with Plaxton President bodies in use in Edinburgh. Lothian 33 (W633PSX) was actually new as an open topper.
Sister Trident 506 (T506SSG) has been only partially converted to open top. It is seen in Edinburgh in August 2014.
Picture ref A4495
Seen on the same day was Lothian's first Trident 501 (T501SSG) fully converted to open top.
Picture ref A4524
Some open toppers start off as fully enclosed, only to be beheaded later in life. A few start as opentoppers, though new builds are more often convertible so that they spend the winter is normal service. Uniquely Tappins provided Oxford with some brand new half open top buses. The front section of the top deck is covered and enclosable. With the access to the rear open deck closed the bus is used on school runs either side of its city tour duties. Tappins 55 (PO55NXU) is an East Lancs bodied Volvo B7TL and is seen near Oxford Station in May 2008.
Whilst 55 was for a time unique, it was followed in late 2006 by similar 56 (PO56JEJ). This is another May 2008 view in St Aldate.