Combining is permissible only when a person is unable to pray Fajr on time and there is real hardship for him to pray Isha on time.

Therefore, you must pray both prayers on time unless you fit the description above.

I live in the UK where isha prayer in the summer becomes very late (reaches 11:40pm) and fajr 3am, so my local mosque is combining maghrib and isha prayer. But the other mosque 5 minutes away from it doesn’t combine (they are both shafi’i madhhab). I have been told by the imam that (combines maghrib and isha) this is permissible for everyone, even if you do not have work in the morning or something. Can you please tell me the rulings on this because I am confused,