[QUOTE=Jonathan Chance]
You seem to keep assuming that Lee would head down the Frederick Road (now Route 15) from Gettysburg and hit Washington City. I’ve never read ANYthing that indicated that was the plan. Or even considered as part of the plan.
Instead I find it much more likely that Lee’s target would be Harrisburg and the ability to threaten (though likely not attack) either Baltimore or Philadelphia. But cutting the railroad junctions at Harrisburg or Erie would have been a real blow to the Union’s ability to communicate/resupply the forces in the trans-Mississippi. While it wouldn’t have prevented the ability of the Union to keep operating in the west it would have made it more difficult.
I’ve always considered Lee’s moves on Pennsylvania in 1862 and 1863 to be political moves rather than military ones. Both had the ability to threaten the Union’s European sympathy and the staunchness of the Union citizenry’s desire to continue the war.
As for the lack of British support concerning CSA victory I refer you to this story from the January 18, 1914 edition of the New York Times which details British Ambassador Lord Lyons complacency and even his chief Lord Russell having told US Secretary of State Seward that it would be a good thing if the CSA won its independence.
There was, in England among the gentry (and above), significant desire to see the United States taken down a peg or two to demonstrate the inherent inferiority of a Republic based on popular vote instead of a ‘Lords’ class of landed group with inherited power.
[/QUOTE]
First of all, I am not the one advocating the Lee would have done anything of the kind. I have consistently said he wouldn’t have done that at all. I think you have me mixed up with someone else. 
Second of all, as is ably argued by others here, the English were not really interested in 1863 in going over to the side of the Confederacy. But that doesn’t mean that thoughts of encouraging that decision didn’t motivate Lee.
According to Bruce Catton, who says it is based upon Lee’s own statements after the war about his purpose, the Gettysburg campaign was about accomplishing two main things: get Hooker away from Richmond, and find a way to supply his army for a little while that didn’t depend upon Virginia (Catton, Never Call Retreat, p. 159 (1965)). You will notice that this would not have entailed any attempt to go in the direction of Washington, D.C. But it also is not intended as a true attempt to gain a military victory. There were thoughts of pressuring the North into a political situation where a negotiated peace might occur, but frankly, that was unlikely to occur anytime after the Emacipation Proclamation, because the South was never, ever going to accept a peace that adjusted the relationship of the landed gentry to their “property.”