The Arab bits breaking away is something which is definitely plausible, but their holding onto even less territory than in the TL where their side _lost_ seems iffy.
When did the revolution happen?
That's a fair criticism, although they do possess Cyprus (which admittedly they acquired after the war) and a lot of Aegean territories so I think it evens out. I suppose an argument might be made that because they weren't partitioned but rather lost territory to rebellion the collective momentum of the Armenians and Arabs (and later Kurds, though they'd initially be loyal) and various religious minorities would overwhelm them in a way that partition did not, but that would be a shot in the dark.
The mid to late 20s, '28 maybe. It was a time of relative prosperity, globally, as IOTL. However that prosperity wasn't spread equally across British society -not that it exactly was in OTL, but imagine even greater stratification therein- and as the losers of the War had to pay some pretty crippling debts that was largely burdened upon the middle and lower class. Successive Labor governments were unable to remedy economic problems, soldiers' wages and veterans' pensions were in arrears and shortages were so bad that limited rationing was still in place for some goods a decade after the war had ended. Nevertheless this was hidden by a veneer of wider affluence and optimism. So when the revolution did happen -in my mind started by a protest gone south- it rather took people by surprise.
The agrarian angle comes from a big distinction from Soviet style state managed collectivization of land, instead subdividing it among rural communities. Of course when this program fell into the wrong hands, as is usually the case with communism, that lead to city dwellers being shipped to the countryside for reeducation.