"These birds fly here from England, and fly back to England."
Translation:Ezek a madarak Angliából repülnek ide, és Angliába repülnek vissza.
That is a question of what you want to emphasise in the sentence. Here you want to spell out that the birds are coming from England, so Angliából is in front of the verb, in the focus, and thus the prefix has to get disattached. Same for the second clause.
If you keep the prefix attached, the focus lies on the verb, making it sound more neutral, "they fly here". But in that case you'll have to restructure the sentence a little: "Ezek a madarak iderepülnek Angliából, és visszarepülnek Angliába."