There is a precedent for U1s on the Western Division.
U1's 31901-4, were tried out by Exmouth Junction (72A) for 5 months from May to October 1961, after which they were returned to Norwood Junction, as unsuitable. For example, Yeovil's 31902 on 1.00pm from Padstow 4 Aug 1964. 31903 at Padstow (between May - October 1961). The three U1s were also tried out at Salisbury (72B) from 5/61 to 9/61, they were:- 31898, 31899, and 31900