If Germany sinks the UK fleet move every warship you can (including French) to the SZ off Wales and build a new one. This keeps enough UK units moving into France to stop Paris falling. The CPS simply cannot afford to match you in naval builds and cannot reinforce the western front as quickly as you can. When the enemy offence has ground to a halt build a large tank stack to finish him off.
The UK units in India really need restricting to balance the game; my suggestion is a maximum of 4 units per turn, of which all but one must be infantry.