Boeing C-17: Fleet of 8. Max capacity 77,500kg/aircraft.
Hercules C4: Fleet of 14. Max capacity 33,000kg/aircraft.
Airbus A400M Atlas: Fleet of 22. Max capacity 37,000kg/aircraft.
How does that compare to road/sea freight?
Well, the maximum weight capacity of a 40ft shipping container is 26,000kg.
In 2017, Dover moved 2,891,500 freight loads. That's 7,920 container loads a day.
So the RAF's efforts would represent a little under 1% of that.
That's great, except that the rest of the UK's ports are carrying over 2x what Dover is, so you're back to square one.