Well this is a topic that has landed literally into my research expertise.

I’m predominantly a First World War historian and my PhD and subsequent book were on exactly this topic.

In short British and French soldiers generally got along surprisingly well overall but there are important caveats to this based upon different years of the war, the changing make up of the British army, and the effect of Verdun & the 1917 mutinies on the French army.

It also must be understood that neither the British or French high commands have much thought to how these armies would interact. So everything that transpired was largely organic based upon the soldiers own actions.

In the opening months of the war soldiers in the two armies never really had the chance to properly get to know each other. The fighting, retreat from Mons, and advance post-Marne were chaotic. The British soldiers at this point were all professionals and had the confidence in their ability you would expect. As a result they were often disapproving of, what they thought, was a lack of professionalism in the French (long hair, dirty uniforms etc) without understanding the Poilu identity. The average British soldier also spoke no French. So communication was hard.

However the original BEF is largely destroyed by Easter 1915. The replacements were civilians. Not soldiers. And they had a crisis of confidence when comparing themselves with the seemingly more accomplished French army before the Somme.

As a result 1916 was a good year generally for relations. The French were adept at recognising when British soldiers were trying to learn and help the war effort even if they lacked skill. Setbacks could be easily attributed by the French to poor leadership in the British army. The French wanted to be ‘good hosts’ and help the British learn, whilst the British wanted to gain experience from the French.

However, Verdun took place out of sight of British soldiers. And they did not understand how the experience both hardened and exhausted the French. Nor it’s role in the 1917 mutinies.

The French, as the war went on, grew increasingly tired of the British apparent lack of learning or even dedication.

So when the British retreated in March 1918, the French Poilus were livid. They saw it as an act of cowardice and ultimate betrayal. The British never fully realised how angry and hurt their ally was; probably for the best.

The eventual victory in 1918, and the nature of it, helped diffuse a lot of that anger and by the war’s end the French had not necessarily forgiven & forgotten, but were more accepting of the British contribution.

The details for all of the above can be found in my book (plus the complicated nature of the American involvement) ‘British, French, and American Relations on the Western Front, 1914-1918’