A number of regiments will be eliminated (including the regiment that famously defended Rorke's Drift). The British will rely, by 2020, on a mixed active-reserve force with more of a burden placed on the reserves:
The key elements of this new structure are the Reaction and Adaptable Forces. The Reaction Forces will comprise three Armoured Infantry Brigades and 16 Air Assault Brigade, trained and equipped to undertake the full spectrum of intervention tasks.
They will also be responsible for generating a Lead Armoured Infantry Battle Group and Lead Air Assault Group, capable of undertaking short notice contingency tasks. Given the high readiness nature of the Reaction Forces, they will comprise mainly regular forces with approximately 10 per cent coming from the Reserve Forces.
The Adaptable Forces will consist of a pool of regular and reserve forces capable of undertaking a variety of roles including overseas engagement and capacity-building, follow-on forces for future medium-scale enduring stabilisation operations, our standing commitments, and homeland resilience.
This pool of forces will be under the command of seven Infantry Brigade Headquarters during peacetime which will vary in size and geometry. These headquarters will also be Regional Points of Contact, responsible for the delivery of homeland resilience and engagement with UK society.
Relying on an expanded reserve force of 30,000 to back the 82,000 regulars is risky for Britain. I assume that this reserve force is a subset of the total army reserves--kind of like our old enhanced readiness brigades of the Army National Guard--because I thought the Territorials were larger than that already. Today, we expect our Guard to provide a pool of 4-5 brigades ready every year out of the 28(?) we have. It just isn't that easy to train all reservists up to standards and keep them fully equipped.
The maneuver forces of the British army will be three mechanized brigades and an air assault brigade.
These forces will maintain a reaction force of a single mechanized battle group (battalion-sized task force) and a single air assault group (I assume that is also a battalion-sized force).
I assume that the other units of the Reaction Forces will need to strip troops and assets to keep the reaction force battalions deployable and so will lose the ability to quickly follow the lead units.
The Adaptable Forces will be a mix of reserve forces in 7 infantry "brigades" that will vary in size--perhaps reflecting the recruiting base of the regiments of the region(?).
Add in a marine brigade in the Royal Navy, I assume.
It may be that the British will be able to maintain in the field only a large brigade-size force indefinitely. This pretty much ensures that Britain can only fight as part of an American-led fight. If this is the fate of even the British army, is there any hope that any Western European army--if it doesn't just want to be a uniformed civil service job program--can escape the fate of just being a tribal auxiliary of the United States Army?
UPDATE: Ah, more from the British. It is interesting that the Adaptable Force looks like paired active and reserve mechanized cavalry and infantry battalions in three separate categories--one doing ongoing tasks, one training, and one training/other (I assume mostly recovering from ongoing tasks?).
So two cavalry and two infantry battalions of this Adaptable Force would be involved in pre-war missions to better prepare allied nations to fight.
The Reaction Force is better than it appears at first glance because the mechanized brigades have five line battalions each, making them rather large brigades. The Reaction Force would surge in if pre-war training and whatnot failed to keep the situation stable. However, the British envision the Reaction Force winning and turning over stability missions to the Adaptable Force again at pre-war commitment levels.
There doesn't seem to be consideration of what they'd do if the Reaction Force fails to win. Unless the Reaction Force goes in with only 5-6 battalions, allowing the other 2/3 of the Reaction Force to rotate troops, sustaining a surge isn't possible.