The UK presents an interesting dilemma for the Allies because their empire is spread out over the entire world. So you want to use a strategy that you think will maximize those units (already on the board) potential while you allow yourself the time to build up your army/navy from London and move out from there.
For the purpose of the basics I’m going to assume that any bid went to Germany and was placed in Afr. I’ll also assume that Russia attacked Wrus, Wrus/Belo, or Wrus/Ukr and Germany successfully countered leaving only Wrus in Russian hands.
UK’s opening moves will also depend on Germany’s other attacks as well as their purchases, NCM, and placements, so we’ll have to take this in a few steps, first Germany bought some naval units such as an AC or moved their Med fleet to sz 13 and second Germany bought all land/air.
While I do think a German naval buy/fleet unification threat/Sealion threat can make its own article it is still fairly common to see Germany at least buy defensively for Sz 5 with an AC purchase so the UK should at the very least be prepared for that scenerio.
In this case attacking the fleet in Sz 5 is out of the question on UK 1 and Germany can also threaten a minor unification with any ships in Sz 13 or a small scale attack on London. So, the UK first and foremost must protect London but with the units already there and a couple US units that can arrive on US 1 it makes Sealion very hard for Germany to pull off. This means you are free to buy whatever you want assuming you won’t be sending all your troops to Alg. I like to bypass going to Alg on UK 1 and buy at least 1 ftr and then some combination of ships, typically something along the lines of 1 ftr, 1 dd, 1 trn (or sub) and then unify my Allied fleets in Sz 8. With the sub/dd/ftr buy and US reinforcements and good purchasing you can make any minor unification/sealion threat futile. It may slow you down a bit in Afr, but the US can really help there but the good news is the UK/US combo should be able to kill the all German ships in Rd 2. The UK takes the brunt of the losses in one or 2 rds of attack while the US can finish the Germans off.
If there is no minor unification move the UK should be set to go to Afr on Rd 2 or simply box in the German navy in Sz 5 by having the combined Allied fleet move to Sz 6 and then you can deal with it at your leisure, usually rds 3 thru 5, when you can add more ftrs for your attack and the US is in position to help you out as well.
There is actually quite a lot of options, which is why this probably deserves its own article.
Now for the case where Germany bought all land/air, you are safe to buy any combination of unit types. I like to go air heavy with the Allies early and sink an unreinforce Sz 5 fleet on UK 2. I don’t like to risk my UK air on the Rd 1 attack of the German fleet. It is certainly a viable option but I just don’t think it is a risk you have to take. I prefer to add some air on UK 1 and overwhelm the German navy in rd 2 (assuming they didn’t add to it on G2).
I might buy something like this, 2 ftrs, 2 inf, 1 rt, but I think 3 ftrs, 1 ftr + navy, or even navy + land are all viable and really comes down to how much help you can expect from the US and where are they going to be moving their ships/troops.
As for British Combat Moves, I don’t think think the British have any "must attacks" in Rd 1 but they could have some nice targets. Any lingering lone German ships should be picked off, Alg is a safe landing spot if your ships are safe from attack in Rd 2 and you expect the US to reinforce you. Egy is a nice target too, but I tend to leave that since it is easily countered on G2 and now you’ve weakend your defenses against Japan and Germany still has access to Afr after G2. I don’t think it is bad to counter Egy if there is only 1-2 unit there but I also don’t think it is a must attack.
In the Pacific the British have all sorts of options as well such as sub vs. sub at the Sol Is., DD vs. trn in sz 59, they can even make a strike at some of Japan’s islands or increase the Sol attack with a ftr and then reinforce Pearl. Agian this could probably be its own article and even lead into a KJF, but I think a good basic move that gives you a lot of options on your future turns is to unify your fleets in Sz 30. This puts Japan in kind of a difficult position in that if they attack they have to divert a lot of air and can leave any survivors somewhat far away from any action in the next round or two.
If they don’t attack then you can grab your inf from Aus and reinforce Africa or the Middle East from the the East as well as from the West (thru Alg/Lib). Any early gains by Germany can be nuetralized by your trns and starting Inf from Trj/Per/Ind, which is why I like to hold off on the Egy counter.
For Non-Combat, it really depends on what your overall Allied strategy is but I think stacking Per with at least 4 inf and an AA, moving the Bom to Cauc, ftrs to Wrus (if not needed to defend London), the Pac fleet to Sz 30, and your Altantic fleet to Sz 12 (or 8 if you didn’t attack Alg) all set up the UK and provide them the opportunity to deter attacks and defend their vast empire for the early rounds as you build up and gradually expand from London.