Ok Issybird, now you made me read more

. About the time Brat went to France: it is mentioned that eighth years have passed since Patrick’s “suicide” and we’re left to assume that The Blitz was afterwards, this means that depending on his timing Brat could have traveled to France before the war broke out. But it is kind of plot hole that the war is not mentioned at all when recounting Brat’s travels.
About the classism, I kind of blotted it out, not being familiar with English history; but yes it’s there for example in the relief of Bee knowing that Peggie having a good horse means her relationship with Simon will fall apart. Now that I think about it, I read it more as the general attitude of the family than an endorsement by the author; furthermore, I can’t tell if this was common with books of the time.
But the moral part, I think at first Brat is clearly in the wrong setting out to deceive an innocent family, he even acknowledges that Loding, “is a swine” for proposing such an action and yet he changes his mind when horses enter the picture; he was faced with a test of his moral fortitude and he failed. But yet his conscience keeps nibbling at him and had not Simon been a rotten apple he would most likely have run away from it, as the Rector told him. And in the end he does the right thing revealing himself as an impostor and allowing Eleanor to take her rightful inheritance; I don’t see him getting a pass since from my point of view he undid the wrong he had made.