Paul has pointed me in the direction of an answer he provided at 16:59, Croston (Post #3321), which everyone - myself included - seems to have missed, when in practice it should have been the current station in play and not West Ruislip (and, later, Pewsey). On behalf of everyone, please accept our apologies
In an effort to correct this,
and to complete my Birmingham set, I shall choose
Birmingham Moor Street. In each case (Pewsey, Croston and BMO) it is possible to travel to a major city whose name begins with "L", even though in practice each of these routes is less frequent than a nearby but less direct alternative between the "L" city and their ultimate destination (Preston, Taunton/Exeter and Birmingham itself).