Some correspondence between the GER, LNER and British Petroleum (BP) concerning the oil siding has survived. The earliest reference is in a letter from the GER Commercial Superintendent, Mr. T. W. Watts, to the Barnwell Junction stationmaster and dated 25 January 1922. From this letter we know an agreement had been reached between the GER and BP for the siding which, at this date, had yet to be laid. The siding was to lead from the Commercial Brewery Company's siding, part which was Company (GER) property, and from within the boundary gate. A plan accompanying the letter highlighted the brewery siding in pink and the proposed oil siding in green. The construction of forty feet of low embankment had been necessitated [as the siding was parallel to the running line of the Mildenhall branch, presumably the embankment was to bring the siding to the same level and thus avoid a short, steep gradient]. Another correspondence records the embankment had been completed by 10 April 1922 but no track had been laid. Traffic to be handled was 'Spirit Tank Cars' and 'Kerosene Tank Cars'. This was the terminology of the time; 'Spirit' meant 'Motor Spirit', commonly known in the UK today as Petrol; 'Kerosene' is the oil better known in the UK today as Paraffin. The Company was to charge BP 1/- (One Shilling, 5p in decimal currency) 'per oil tank wagon or truck' and the siding was to be operated by the Company but under supervision of a member of BP staff. The latter was necessary as tank wagons had to be positioned in a certain order according to their contents.
1965 1:2,500 OS map showing the oil siding and the truncated siding into the brewery siding. By this date the brewery building had found a new use as a furniture depository.
A memo from the Operating Department, Cambridge, to the Barnwell Junction stationmaster and dated 12 July 1922 informs us the siding had by then been completed to the satisfaction of [the Company's] engineer. The wording of this memo implies the siding had actually been constructed by BP but it more likely means it was constructed by either the GER, or a contractor approved by the GER, to the requirements of BP. Things did not, however, go to plan for on 29 January 1923 BP wrote a letter to the LNER complaining that the railway was simply leaving tank wagons on the siding in no particular order and in the wrong positions for unloading. The problem obviously occurred because BP appears to have overlooked (or its staff were simply not bothering) the agreement for shunting to be supervised by its staff for the following day, 30 January, Mr. W. Gentle of the LNER replied [on GER notepaper] pointing out the agreement in no uncertain terms. Mr Gentle's letter goes on to mention, with specific reference to the previous day, that 'a lot of unnecessary work was caused changing the tanks over'. BP had no means of shunting of their own so obviously the LNER was having to send a locomotive down to Barnwell to sort things out. There was no further correspondence on the subject so presumably following 30 January 1923 everything went according to plan.
Aside, the system for tank wagons on the siding was Spirit Tanks at the bufferstop end and Kerosene Tanks nearest the entrance gate. One may therefore wonder why tank wagons were not marshalled accordingly before being sent down from Cambridge. A clue may lie in BP's letter of 29 January 1923 in which they advised 'For your guidance, Spirit Tank Car labels are marked in blue type, at the top of card, either B.P.I or B.P. III, while Kerosene Tank Cars are marked in yellow type either R.S., W.M., T.V.O. or P.V.O.'. The implication is that railway staff were unfamiliar with the codes used on BP's tank wagons or labels, although this must be considered highly unlikely.