The British will pretend that having a smaller military is irrelevant, despite admitted shortcomings:
In the future, the British military is intended to be leaner, more able to concentrate on specialization, and more reliant on reserves.
Crucially, planners have decided that the military will no longer be able to mount the sort of long-term operations conducted in Iraq and Afghanistan. Going it alone in the form of the task force that liberated the Falklands in 1982 will also no longer be an option.
Yes, they'll specialize on weak enemies. Oops. The French drew that European mission (Mali). What else is there? Weak naval opponents? Good luck with that.
It had better be a weak naval opponent since the British are relying on the French to provide a carrier while Britain lacks one. The British say that they can't go it alone in a Falklands II, but the French will provide the carrier.
Wait. What?
Never mind.
The British army will be limited to sustaining a large brigade in combat for years at a time. So they could, with the 2% rule, pacify any country of 400,000 people or fewer with their own resources. If Luxembourg becomes difficult, Britain will need help.
The British try to tell themselves this won't matter since they and the French will pool resources. So combined, they'll be a middling power unable to project much power beyond 500 miles and reliant on American military and logistics support.
What could possibly go wrong?