Probably you do not need a sticker. UK is a signatory of Vienna convention on Road traffic (list of signatory). The last annotation from UK were done this year (2019, mostly about status in Gibraltar, the Bailiwick of Guernsey and the Bailiwick of Jersey), so it seems that UK accept it.
The annex 3 defines the country identification, either with the sticker ...
Temporary Importing a Car in Ukraine
Regardless who owns the car, the documents required to cross into the Ukranian by car are the following:
Compulsory personal documents: international passport, visa if needed
Vehicle registration certificate
International driving license
“Green card” international insurance policy
Upon entry, the customs officer will ...