I haven´t been at this spot myself but looking at google map the most obvious spot seem to be Earnslaw Car Park on B4218 Wyche Rd in Upper Colwall. It has a gate that may bee closed during night but if you are not in your car when the close what shall they do? We have done like that a few times on our travels in UK. Once we were ordered to move by some sort of parking warden. Another time we got some angry comment from the lady opening up in the morning but I simply explained that we had been on a walk and came back much later than expected. And we also told her that we had no problem spending the night on the parking lot (which was exactly what we had planned the day before but did not say). Others have just said that the lock now and we just said OK, that´s fine with us.
Another option is the carpark by Peachfield Rd down below the previous. No gate and no signs of any kind.