Well, my Driving Instructor has information from people he knows in the Bus industry that what we thought were brand new buses (60 Plate), in fact were bought after they had been in storage for three years in East Anglia, but hadn't been registered as they couldn't sell them when built!
There's a few buses like that, mainly the Plaxton Primo. You can still buy a Plaxton Primo today on an 11 reg, but they haven't built one for years. The company who built the chassis (Enterprise) went bankrupt a few years ago, but Plaxton still had a large number of Primo's in storage that were unsold. A decent number of these have since been purchased by Reays Coaches in Cumbria, for use on their CityHopper bus services in Carlisle (started in October 2010), attempting (and failing) to compete against Stagecoach's Carlisle Citi network (established in summer 2005).
The BF registrations on the Plaxton Centro's at BT are there because they were registered by Volvo at their Coventry centre (opened in 2010 I think).
As for new buses for Blackpool, I'm not aware of any plans to purchase brand new vehicles. Most of the standard public services now should be operated by low floor buses, the oldest being 12 years old. The step entrance buses nowadays should be restricted to schools and special duties only where possible, but as you get with any company, they will also provide as a back-up fleet to cover breakdowns etc.
All I can really say for now, is new (or 2nd hand) double deckers could be entering the Blackpool fleet in a few years. CitySightseeing tour contracts, when renewed, will have full wheelchair accessibility written into the contracts, so those D reg Leyland Olympians will have to go. BT could obviously run the service as their own open top service, with the Leyland Olympians in their own livery, but to keep them in CitySightseeing livery, with the brand, they should be operated by low floor vehicles upon contract renewal.