Is a TCO authorisation issued by EASA required to perform commercial air transport operations to the United Kingdom?

No. As a result of the decision of the United Kingdom to leave the European Union, foreign air operators are no longer required to hold an EASA TCO authorisation  to operate to the United Kingdom and EASA does no longer have a mandate to issue authorisations for this purpose. 

For further information, you may wish to contact the UK Civil Aviation Authority via TCO [at] caa.co.uk (e-mail) to enquire on UK TCO related issues.