London System counter against Philador Defense

    But the London System is a d4 opening. The Philidor defense is in response to e4. Are you sure you're not mixing up openings here?

Play Nf3 instead of Nd2 to stop e5

This is not a Philidor, but the nomenclature is irrelevant.

Do not play the London on autopilot. Your opponent's moves are just as important as yours. You have learned that in the London "this pawn goes here, the other goes there, i set my knights like that"...etc This may work great against a certain Black setup, and horribly against another one. Playing a 'system opening" does NOT mean that you can play the same moves, with the same order, against any opponent moves all the time. See the opponents' move, try to understand what it's trying to achieve, and act accordingly.

1.d4 Nc6 2.Bf4 Nf6 3.e3 d6 4.Nd2 e5

True 4.Nf3 does stop 4...e5, but it allows black to chase down the bishop starting with 4...Nh5, e.g. 5.Bg5 h6 6.Bh4 g5 7.Bg3 and now since the bishop cannot escape anyway, black does not have to play 7...Nxg3 yet, but perhaps 7...Bg7.

It might be that Bf4 was already slightly inaccurate, since it allows black to answer d4-d5 with ...e7-e5, instead of having to move the c6-knight right away. 1.d4 Nc6 2.Bf4 d6 is another move that highlights this drawback. Whether Bf4 discourages ...e7-e5 or in fact encourages it is open to debate. It's certainly something to think about.

Thanks everyone, helpful stuff.