POW Escapees

[Warney]

Dear list, I am trying to retrace the steps of my grandfather Signalman Private Harold Swallow (204193). Harold was taken prisoner of war around 16th April 1918 (the date he was posted missing). Harold was serving in 1/7th Battalion Prince of Wales (West Yorkshire Regiment) - although at various stages he was asigned to the 5th and 6th Battalions (I believe all in the 49th division).

Harold eventually escaped from the POW camp where he was stationed (elder members of the family state via the sewarage system into the Netherlands. Indeed I have a copy of his "controlepas" from his time there - dated 13 Nov 1918 )

At around the time of his capture the 49th Division was involved in the great German offensive at Lys (possibly The Battle of Bailleul). My question is does anyone know where prisiners from the Lys area would have been taken at this time - and are there any records available?