Is the agreement of Muslims in Britain on performing the 'Isha prayer and delaying the Adhan for Fajr and Imsak in Ramadan considered a consensus that obviates the need to ascertain the time of prayer and Imsak, and should one continue to perform the 'Isha prayer individually according to the official time, or adhere to the congregation?

It is not correct to fix a specific time for the entry of the 'Isha prayer, such as an hour and a half after Maghrib; because its time begins with the disappearance of the red twilight, and this varies with the seasons. If it becomes clear to the worshiper that the congregation is praying at the correct time, then he should pray with them. But if it becomes clear that they are praying before or after the time, then he should pray at the correct time, even if alone. And whoever cannot ascertain the time through personal effort may follow someone he trusts, and should rely on the later time for prayer if there is a discrepancy in timings.