Stainer was Chief Mechanical Engineer of London, Midland and Scottish Railway (LMS). Backed by Sir Josiah Stamp, Chairman he introduced over 11 locomotive designs which were a strong influence on the standard design later adopted by British Railways. Stamp had spotted Stainer following a long and successful career at the Great Western Railway, where Stainer had supported Christoper Hinton who would go on to become an immensely successful nuclear engineer. One of his LMS locomotives, the Princess Coronation Class 4-6-2 No.6220 Coronation set a new British record of 114 mph, beating the previous record set by Nigel Gresley's A4. During the Second World War he worked for the Ministry of Supply before retiring in 1944. After which time, he was elected a Fellow of the Royal Society and President of IMechE.