I have a little more information from another forum,
The War Diary for 298th Brigade, RFA you mention indicates that on 21 March 1918 the Brigade was in positions in the Montescourt area. Early that morning it was ordered to fire on a line between Sabliere Farm - Manufacture Farm. The Brigade Wagon Lines were heavily shelled with 40 horses, one officer and four men killed and six wounded.
That would definitely fit with my Hugh Quigley who's rank was Driver, it is also fits nicely with the first day of the German spring offensive (Operation Michael) as they pushed South from St Quentin into the Montescourt area where Hugh and the 298th where positioned.
I am still a little confused though, my lack of knowledge of Army structure and reorganisation doesn't help.
The 298th left the 59th Division to become Army Brigade in 4 April 1917 and became part of the Fourth Army. I have been reading up on Operation Michael and the Battle of St Quentin, (21 - 23 March 1918) and the order of battle for this period only shows the Third and Fifth Army being involved the Fourth Army does not seem to become involved in the area until the Battle of the Avre, (4 April 1918).
To confuse things even more it says:
"Lieut-General Sir Hubert Gough was relieved of command of Fifth Army between 5-6pm on 27 March 1918. He was replaced by Sir Henry Rawlinson, hurriedly recalled from his position as British Permanent Military Representative to the Supreme War Council. Sir Henry brought in his own staff and the command became Fourth Army." Source:
http://www.1914-1918.net/bat22.htmAm I right in thinking from this that the Fourth Army had ceased to exist sometime before the 21st March 1918 and was reformed on the 27th March 1918.
If so could the 298th have been attached to the 59th Division or 9th (Scottish) Division on the 21st March. Both were at the Battle of St Quentin on the 21st with the Third and Fifth Army.