In the name of Allah, the most Beneficent, the most Merciful.

Answer

There are differences of opinions regarding the distance allowed to take the deceased from one place to another.  One view is 48 miles whilst another is one or two miles.  Anything above that is Makruh Tahrimi.   (Raddul Muhtar p.146 v.3)

Before answering the second part of the question it would be preferable that I mention who is the most worthy to lead the Janazah Salah of the deceased.  The ruler is the most worthy to lead the Janazah Salah of the deceased.  If he is not present, then the governor or ruler of that particular place is worthy to lead the prayer.  Then it will be the Qadhi (judge) then the imam of the locality then the guardian (or the family member responsible for the deceased) provided they are male.   (Raddul Muhtar p.119-p.120 v.3 & Nurul Idah p.128)

The one with the most right to lead the Janazah Salah may give permission to others to lead the Salah.  And if the one with the lesser rights leads the Janazah Salah without permission, then the one with the most right may repeat the prayer if he wishes and the people who prayed the first time with another imam are not required to repeat the prayer should it be repeated.   (Raddul Muhtar p.123 v.3)

Now coming to your question, if the wali of the deceased such as the sons read the Janazah Salah in England, then no one will be allowed to repeat it.  However, if any of the wali (such as the sons) did not read the Janazah Salah in England and took the body to Pakistan, then they may repeat the Janazah Salah however, taking the body all the way to Pakistan is Makruh Tahrimi. It should also be remembered that if one of the sons read the Janazah Salah in England the other sons will not be able to repeat the Janazah Salah in Pakistan. Similarly, the imam of the local mosque will not be allowed to lead the Janazah Salah in England as he is more worthy than wali.

Only Allah Knows Best

Mohammed Tosir Miah

Darul Ifta Birmingham