I haven't played the new patch yet but here is some stuff that used to work:
-
Import artillery and build a shit-ton of cannon artillery units. This will improve your army massively.
-
Try getting a defensive pact with Russia.
-
The moment that the British land, do your own naval invasion in the same spot. This usually splits their frontline and confuses the AI.
-
You could avoid naval invasions entirely if you keep sending 1-ship fleets to intercept their invasions. Naval battles take a lot of time event if it's a huge British fleet vs 1 junk. While this is happening, do a naval invasion in one of their colonies in Africa to get a ticking war score.