Potential Elizabeth Line exploit?

Had an overall enjoyable game of Mornington Crescent yesterday with friends, but one of the more experience players used a move that has potential to break the game.

I used the Cholmonley-Warner diagonal to play Bond Street from the previous play of Bank, but then the player after me said that my use of the Cholmonley-Warner to Bond Street diagonal allowed them to completely negate the Elizabeth Line gambit and play Slough! I couldn't believe it, as I knew the next round would allow them to just implement the Lancaster Sacrifice and get Mornington Crescent!

This can't be legal play as it breaks the game, right? Or am I missing something?