I am part way up the Napton flight tonight, just below lock 14. Oxford was an ambition, plenty of time, and noted the “not exceeding 50’ boats” winding in Nicholson’s which seems to be above Isis lock. Looking at Google satellite view, there seems to be room to wind below Isis lock without going down Sheepwash channel to the Thames (boat is 56’) or what’s to stop you entering the Thames under the railway bridge, winding, and returning to Isis Lock?
I am aware of one day licences for the Thames purchasable from lock keepers but no lock is involved if wind and return? Or am `I being stupid.....