John Lewis will definitely cover it.
Mine developed the same problem a year and a half into warranty, and they took it in and swapped the top cover with no questions asked.
Be aware, it takes time though! While the job itself only takes about half an hour, my macbook was away for over 3 weeks.
Even then, it had to go back again as they'd fitted the wrong part!
If you do have an Apple Store near you, make an appointment first, and take it in, they should repair it either while you wait, or by the end of the day.