LNER Class A4 4468 Mallard steam engine

Number 4468 Mallard is a London and North Eastern Railway Class A4 4-6-2 Pacific steam locomotive built at Doncaster, England in 1938. While in other respects a relatively typical member of its class, it is historically significant for being the holder of the official world speed record for steam locomotives.

Normally it's located at York Railway Museum, but here at Didcot Railway Center it's as special guest train.

http://en.wikipedia.org/wiki/LNER_Class_A4_4468_Mallard

Left of the Mallard is a GWR 2-6-0 engine no. 5322 from 1917.