I'm at a loss as to how a paragraph concerning John Roebuck's self destruction relates to my assertion with regards to Confederate battlefield success or, perhaps more importantly, the Roebuck Motion in 1863 relates at all to the main point at hand of British intervention in the Fall of 1862. As for the situation at hand then:
Two sentences after your screencap of page 290 ends, the source says "British observers were shocked by the South's poor showing, for they had hoped for another military success that would have compelled the North to accept mediation." This source shows that the British considered offering mediation, not armed intervention in support of the Confederacy.
British would-be interventionists should not have been surprised that the Confederacy lost at Antietam. Lee had no chance of winning at Antietam and should never have fought the battle. Any other commander of the Army of the Potomac probably would have crippled the Army of Northern Virginia.