I think you will find it was the 9th Lancers that accompanied Haig.
\below is some info from Wikipedia for 17th Lancers in WW1
First World War[edit]
Further information: British cavalry during the First World War
At the beginning of the First World War, the 17th Lancers formed part of the Sialkot Cavalry Brigade of the 1st Indian Cavalry Division.[21] The regiment landed in France in November 1914. In the static warfare of the Western Front, the 17th was often restricted to infantry roles, such as the occupation of trenches.
The 17th was eventually used in its conventional cavalry role in 1917, at the Battle of Cambrai, which happened to feature the first large-scale use of tanks. In 1918 the 17th was transferred to the 7th Cavalry Brigade, part of the 3rd Cavalry Division. That year the men got another chance to prove their worth as a cavalry regiment during the last-gasp German Spring Offensive. The 17th functioned as mobile infantry during the attack, plugging gaps whenever the need arose, both as cavalry and as infantry. The 17th also saw service in the British counter-attack, including the Battle of Amiens.
After the signing of the Armistice on 11 November 1918, the 17th remained in continental Europe, joining the British Army of the Rhine in Cologne, Germany. The regiment then served in County Cork, Ireland, where it operated against the Irish Republican Army during the War of Independence. In 1921, the 17th had its title altered to the 17th Lancers (Duke of Cambridge's Own).
