Grovelling apologies but I gave some incorrect information. The "Tousanticovid" app that acts as your "pass sanitaire" (vaccine passport), CAN be downloaded in UK. (My friend said he was referring to another attestation needed in connection with his residence permit.)
Don't worry, it is in English and is easy to use. There have been rumours on Twitter that the UK QR code is not always recognised. If this should happen, simply take it to any pharmacy and they can change it for the European QR code.
Just to underline the point, it is OBLIGATORY in all restaurants, bars and cafes.