In 1993 two, nos. 55021, already in departmental use, and 55023, were transferred away from OOC to Bletchley for use on the Bletchley to Bedford line and the other diesel powered lines then under North London Railway's control. In due course four Class 121s were to be resident at Bletchley nos. 55023, 27, 29 & 31. 55023 was repainted in dark green in 3/93 and 27, 29 & 31 into NSE livery.

The units have also proved to be useful as route learning vehicles and/or Sandite units. The following were converted to that use :- nos. 55020, 21, 22, 24, 25, 26, 28, 30, 32, 33 & 34. 55035 was in departmental use from 1978 as a route learning car until scrapping in 1992.

Sandite 977858 (set 960010) was given a maroon livery. It is seen below passing through Amersham, returning to Aylesbury on the 4th Dec. 01. Picture by Colin Cooke.

After sandite / route learning some have went on to other work. Below is 960011 (977859), seen below whilst at Skegness during the morning of Friday, February 23rd, 2001. Thanks to Peter, Lincolnshire & East Yorkshire Transport Review, for the pic. It films the rail system for Balfour Beatty Rail.

977860 (ex-55028) had it's sandite gear removed, a basic internal revamp, body repairs and a repaint at the Midland Railway Centre during Sep. - Dec. 2001. From there it went to Ashford for mechanical work before returning to the National Network as a second camera for Balfour Beatty Rail. The two vehicles are only leased by the firm, they are still owned by Railtrack who demanded they were painted into their livery. The decals on 977860 were to be applied at Ashford by the same firm that did the first one so that they matched. Below it is seen leaving the C&W shed at Butterley in the fading light of the 20th Dec. 01.