I don't know what Apple's policies are in the UK.
But here in the USA, a 2017 MBP has had the warranty on the keyboard extended to 4 years due to the failures of the butterfly keyboard.
Under the above program, a 2017 unit should still be covered.
Do you have a brick-n-mortar Apple Store (that is open) within reachable distance?
If so, make an appt and bring it into the genius bar WITHOUT DELAY.
Time is of the essence here (if they have the 4-year extended warranty there, too), and your time is running out.
If you DO NOT have an Apple Store nearby (or if it's closed due to the virus), call Apple directly.
DO NOT call a 3rd-party service center or provided.
CALL APPLE SUPPORT (and no one else).
Explain that you have a butterfly keyboard failure.
They may offer to send you a prepaid shipping carton, and return the MBP to one of their repair facilities.
Be aware that the "keyboard" (per se) cannot be replaced on a 2017 MBP.
If there's a keyboard failure (even for only one key), the ENTIRE TOP CASE of the computer must be replaced. That's why it must be "sent back".
Again, if they have the extended keyboard warranty in the UK, your time is running out.
DON'T DELAY -- get this done!