British Embassy in Ukraine states that Ukrainians cannot travel abroad without a separate permission from the Ministry of Foreign Affairs.
This is stated on the embassy's Facebook page..
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The British Embassy reported that they undertake to assist in obtaining such a permit if data on the planned trip will be submitted no later than 72 hours before the departure of the charter flight or crossing the ground border.
The embassy opened the possibility of such applications for leaving Ukraine only to owners of the British Biometric residence permits and noted that it could not help those who have visas of any class, but do not have BRP.