However, I understand that you can place them only where you can recruit them? So while you have full flexibility with "green" English, places for "Blue" are limited?
And second question immediately - what if all reinforcing shires are occupied by Vikings - what happens with fled British units?
The rules say English fled units go on “any English-controlled Reinforcement City Shire”. There’s no mention of restricting it to shires where reinforcements of the same type can appear. As for the second question, the rules are quite explicit: If no spot is available, the units stay in the fled units area.