Transport of Delight Blog is this fantastic BusTubeTrain vehicle. Apparently it is a Daimler DMS owned by the Epping and Ongar Railway.
The rear(?) train wheels are add-ons, covering the busses rear wheels. Inside, it is possible to walk from one end to the other.
Ingredients for a model: Diecast bus. Diecast tube train. RTR DMU
Method: Take deep breath and grasp your saw handle firmly...
My mate Tim describes this as "Perfect integrated transport" !