The newly completed 79xxx sets were tested on various lines in the Swindon district including the M.S.W.J. line to Andoversford, the closed Malmesbury branch, and on the main lines to Bristol (Dr.Day's Bridge), out via Bath and back via Badminton. This British Pathe clip features a period newsreel of a set on test.
The first vehicles worked north to Leith Central during the w/e 25th August 1956. Initially termed "Inter-urban", this was soon changed to "Inter-City" long before that branding was used for main line express services.
Most 79xxx vehicles were introduced to Edinburgh to Glasgow services in January 1957 allocated to Leith Central depot. The usual E.& G. formation soon became a six-car set with the two trailers together in the centre of the train, flanked by the intermediate power cars and then the leading power cars on the outer ends. The class usually stuck to this route but did appear on other services from time to time.
The first six three-car sets worked their first three years on Western Region on Birmingham - South Wales services. They were introduced to the WR in the Summer 1957 timetable on Birmingham - South Wales services. The frequency and timings were improved over the previous steam service, but slower than those on 1934 acheived by the GWR introduced AEC railcars. The new service comprised four trains each way (SX), two running between Snow Hill and Cardiff, one to Swansea and one to Carmarthen. A new feature was morning and evening trains between Birmingham and Swansea on Sundays. All the services ran via Stratford-on-Avon. The weekday schedules were slowed down by all the westbound and three of the northbound services being routed via Hatton North Junction to bypass the Henley-in-Arden interval service. The best times between Birmingham and Cardiff were now 150 minutes (the 8.25am westbound) and 152 minutes (5.30pm northbound), in 1934 these were 142 minutes westbound and 143 minutes northbound.
The Winter 1957 timetable WR saw services continue as the summer timetable with just a slight revision of intermediate timings and they now also ran on Saturdays. The 8.25am from Birmingham and the 8.05am from Cardiff now called at Stratford-on-Avon, meaning only one train in each direction didn't make that stop. From September 23rd until December 15th 1957 there was engineering work between Honeybourne and Cheltenham, meaning services were diverted to run via Evesham (over a new connection provided for the purpose) and Ashchurch in both directions and were retimed.
The 47 mile Edinburgh to Glasgow line was Scotland's premiere service, it was intensively worked and at the Glasgow end had a long climb out of Queen Street station. These conditions took their toll on the units and they were displaced from 1971 by the Class 27 push-pull sets. Although it seems like a short lifespan for the service, fourteen years was quite impressive as the line does have a quick turnover of vehicles. The Class 27s only lasted eight years until replaced by Class 47/7s, which only lasted 11 years until replaced by 158s, etc. A set did a trip to Wick / Thurso to test their suitablility for transfer to the Far North line, which didn't come to anything. All were withdrawn by 1972 except for four cars transferred to Ayr. Disposal was a long process, the vehicles were stored en-mass at Millerhill for a while and slowly migrated south often stored at places en-route to Snailwell where most were cut up. Some went via Polmadie depot for component recovery.