The sets were originally designed for a through South Coast - Wales service, and initially consideration was given to building them with diesel electric transmission. Plans for a through service from Brighton were abandoned because of the SR`s resistance to DMUs, but they did manage to make it to Portsmouth on services from Cardiff and Bristol.
The sets were introduced on Western Region services between Swansea, Cardiff, Birmingham, Derby and Crewe, and on the Cardiff to Bristol route. Displacement saw them allocated to Reading for working "outer-suburban" services out of Paddington to Oxford and Newbury. Next stop was Cardiff for working secondary services from South Wales, such as to Bristol. In 1977 they were displaced again, but this time to store at Barry, as the WR had no further use for them. However in April 1977 the ER Chief Passenger Manager saw the opportunity to improve the level of comfort on his Trans-Pennine services by integrating them with the Class 124's, and approached the regional CM&EE. At the time there was a rolling stock rationalisation going on, and this would concentrate the two similarly engined classes in one place. Agreement was reached in May 1977 and the first three car set, W52092, W59820 & W52097 was transferred on the to Hull Botanic Gardens on the 5th June. 12 four-car diagrams were subsequently introduced, and although resisted initially, the classes were mixed as required.
That year saw the last of the through Hull to Liverpool workings, and the sets settled in to working the "South Trans-Pennine" route from Hull - Doncaster - Sheffield - Manchester, and occasionally to Leeds. Having Leyland Albion engines they were considered non-standard and had not been included in the refurbishment programme. In May 84 these services went over to loco-hauled trains, meaning withdrawal of the two classes. On the 4th May E52089 was the last vehicle to undergo an engine/gearbox change, only 10 days before scheduled withdrawal. E52098 and E52100 were the two power cars on the last booked working on the 13th, however the final working was E52090 and E52096 on an additional booking, the 06.35 Cleethorpes to Doncaster on Monday 14th May.
In July 67 the BRB approved practical testing of a Rolls-Royce Dart gas-turbine engine on a Class 123. The engine and transmission were to be supplied at Rolls-Royce expense. This class was selected because of its B4 bogies, although it was mentioned that when ready in early 68 that it would not run at speeds higher than 100 mph. No further information can be traced on this, so we assume that the project was abandoned.
Buffet car 59831 was converted to run in a Class 309 set after accident damage left 309 616 without a buffet car. Renumbered 69108, it was withdrawn in April 81 after it too received accident damage.
The image shows set E52090 + E59819 + E59838 + E52096 at Morecombe Promenade on the 27th August 1982 after arriving from Leeds. Robert Frise.
Rick Squirrell notes: "As delivered these were given numbers 511 - 520. I first encountered 2 of these distinctive sets at Portsmouth Harbour on a Cardiff working when they were brand new; they looked very important alongside the green and plain blue of the electrics. Upon transfer from Cardiff to London (Reading) they soon became L701 - L710. (Many years later that series was re-used for class 104 sets running from Old Oak Common on the Gospel Oak - Barking route. Those 104's also appeared in the Thames Valley at times. I was rather surprised to encounter one on an up Slough stopper one day!).
While on the WR the sets stayed more or less in correct formation which was:
511 / L701 : 52086 + 59818 + 59235 + 52096
512 / L702 : 52087 + 59819 + 59236 + 52097
513 / L703 : 52088 + 59820 + 59237 + 52098
514 / L704 : 52089 + 59821 + 59238 + 52099
515 / L705 : 52090 + 59822 + 59239 + 52100
516 / L706 : 52091 + 59823 + 59828 + 52101
517 / L707 : 52092 + 59824 + 59829 + 52102
518 / L708 : 52093 + 59825 + 59830 + 52103
519 / L709 : 52094 + 59826 + 59831 + 52104
520 / L710 : 52095 + 59827 + 59832 + 52105
Upon withdrawal of the buffet cars L706 - L710 lost 59828 - 59832 to become 3-car sets. In their later days it was not uncommon to see odd cars coupled with a complete set to form a train of the required length. I have records of two 3-car sets coupled, of a 4-car coupled with two coaches from another to form a 6-car, and of two three-cars units plus two cars from a 4-car unit coupled between them to form an eight car train. Another formation noted was two 3-cars coupled with an odd driving motor (DMSK) to form a seven car train. But despite these oddities the sets tended to stay correct and were remarshalled correctly after being split.
One of the less common (and less popular) workings was the evening Paddington - Bourne End train which should have been 8-car Inter City stock, 7 after the buffet was withdrawn, but was very often a 4-car 123 coupled with a 3-car 117. I have noted this on one occasion formed of 3-car 123, a Class 121 bubble car and a 3-car 117.
These units carried bodyside destination boards for a few years - this is possibly unique for British DMU stock though was a feature of WR loco-hauled expresses at the time. Clearly they wanted the DMU sets to look like and have the same feel as their hydraulic-hauled expresses! A yellow board (about 18" square) was clipped to the lower panels midway along each driving car (not the trailers so far as I recall) with black lettering proclaiming PADDINGTON OXFORD or PADDINGTON NEWBURY with one name above the other. Special clips were fitted to the bodysides for these boards which were later removed. Pictures of them in service with those boards seem to be rather elusive however!"