Inflation isn't a temporary issue, inflation may return to a more manageable level but the 10% is baked in now and won't vanish even when inflation settles.
Imagine pay has risen, on average by 2% p/a over the last 5 years, while inflation ran a 3% for years 1-3, 10% year 4 and 2% year 5. We'd get the following:
Pay (100 base) = 102, 104.4, 106.12, 108.24, 110.40
Costs (100 base) =103, 106.09, 109.27, 120.2, 122.6.
Inflation in year 6 is expected to be 2% again so pay will need to rise by around 14% in year 6 to reach parity.
More than a decade of wage suppression has reached a tipping point and will now have to be corrected. Nobody, AFAIK, is talking about or pursuing a policy of deflation so the only way is for pay to increase.
But pay isn't the only issue with Royal Mail and as had been explained on this thread numerous times the 9% had lots of unfavourable conditions attached.
The crux of the issue here is that the Royal Mail has been bought by people who clearly didn't understand the USO attached to the purchased and instead so it as a way to make some fast cash for.
Really the government should be getting far more flack than it is for a) selling it off to people who clearly couldnt handle the RM in the first place and b) failing to speak out about how the current owners of RM operate. Although, given the government's handling of the RMT, I'm not surprised they're staying quiet.