Just been doing my usual bit of research and found two possibilities for local showers
. There's a place on the NE side of Canterbury called Kingsmead Leisure Centre and they have separate showers but would charge £5.00 as this includes a swim too (51° 17.174' 1° 04.995').
Also, the M20 junction 8 Maidstone Services has free showers. Just hand your keys in at the WHSmith shop, have a shower then return to collect your keys. It is 35 mins away from the pub though (51° 16.021' 0° 36.870').
I've phoned the pub and they have accessible toilets with sinks only which also have an outside door so accessible for campers. They're also setting up an external tap so we can get water.
I'm going down Friday and making a weekend of it too