Is it obligatory to adhere to the sunrise time recorded in booklets as the determinant for the end of the Fajr prayer time in Britain, especially with the cloudy weather that prevents visual confirmation, or does Fajr end before this time?

The time for Fajr prayer is from the appearance of true dawn until sunrise. The report of a trustworthy Muslim, if based on knowledge, is sufficient for knowing when its time begins and ends, according to Ibn Qudamah in Al-Mughni: "And whoever is informed by a trustworthy person based on knowledge, should act upon it, because it is religious information, and the statement of a single person is accepted in it, just like in narration." Therefore, if those responsible for preparing this booklet are trustworthy Muslims who report based on their knowledge, there is no harm in following their report.