The Battle for France didn’t end at Dunkirk
The title of Saul David‘s “Churchill’s Sacrifice of the Highland Division” is possibly erroneous, the book doesn’t come out for what happened to the 51st Highland Division in June 1940 as being a political gesture of allied solidarity on the part of Churchill.
It is certainly the fullest account of the 1940 campaign of the 51st Highland Division, expanding hugely on Eric Linklater‘s HMSO publication in 1942 (which perforce had to be limited for security reasons). The Highland Division was in the Maginot Line attached to the French Army when the German assault started on 10th May 1940 and so wasn’t with the rest of the BEF. By the time the ferocity and direction of the German plan was understood by the French & British High Commands most of the German Army was between the 51st Highland Division and the BEF; so there was no real decision to sacrifice them on the part of Churchill. Saul David makes this readily understandable in his narrative, although he does highlight some of the points where a clear directive to withdraw them could have made a difference. However these would have to have been ordered by French Generals as the Division was part of the French IX Corps and under their command.
What is remarkable is that the Division only surrendered when surrounded and out of ammunition nearly a fortnight after the Dunkirk evacuations were complete.