If after clarification it still needs changing, and it's proven by the facts it needs doing by the dealer, rather than by guess work.
You are within your rights especially if Citroen U.K do not pay for it, to tell the main stealer to not proceed with the repair, and go to an independent.
There are many independents with a vast range of experience on older (classic) Citroen's and new, and they can even be ex main dealer technical staff who have set up their own business, who will do the job cheaper, and will care for your car more, and might be able to get this part it requires, from G.S.F etc, and at a cheaper price than the main stealer!
Try to get Citroen U.K. to swallow the cost, as it is a recent car, with a safety related problem, which in the U.S. would be called a "Lemon" it's not good P.R. for Citroen to not do this job, and after all it's like the pump isn't fit for purpose, if it's not man enough for the job, and they have admitted as such then they should pay for it!
There are too many wearing the above, who are made to ensure the most amount of money they can get comes into the dealership, and they are on bonus to do this!Picked it up Saturday. Guy dealing with me was, I think, a service manager. Well, at least, he wore a shirt and tie and was based in the service department!
They care more for the pockets than for the customer at times!
Did he have a badge on saying service manager, because he could well be from a non technical background, and be just a pen pusher who does not check things correctly, and might not even be a service manager, and just a service advisor!