Looking at the map and as I'll becoming from the east and you the north, so either we meet up just east of Tewkesbury not sure where or west of Gloucester at this car park at N 51° 52.145 W 002° 19.392?
It is in an old railway tunnel and it was far from obvious where the access was. One end was in some bodies back garden and the home owners were watching us, the other end had no easy entry. We sent a mail to the FTF asking for help, his answer was too late to be of any use. We did drive back past later on and even knowing where to go we thought the access point looked like private property.
The cache had been found before we got there but as TJ says, you have to cross private land to get to the old cutting and onto the tunnel - makes me unsure about this one.
We did do 28 days later, so I could find it - thank you TJ