I've started digging around at travel to Cambridge so thought I could help you all out (for those going by train).

Train to Cambridge, these all look to take 1 hour 30.
Then you can get a bus from the station to Cherry Hinton Hall (festival site). You can go for free is you download and print a bus ticket from here: https://www.cambridgelive.org.uk/tickets/events/complimentary-bus-voucher-cambridge-folk-festival-2019 (on the right are options of which day you want to book, it says at time 23.00 but think that's a glitch. These seem to take 15-30 mins.
From the main festival site you can then get a free festival bus. These are every 15 mins and then take 10-15 minutes.
Showing your pass that was forwarded to each of you and you have printed you can then get on the campsite, set up your tent (potentially in an allocated place) get into kit
Then get the free festival bus back to the festival site

For your info: Bus timetables https://www.cambridgelive.org.uk/sites/default/files/public/wysiwyg/Folk%20Festival%20Leaflet%202019%20-%20WEB.pdf

Please note you can download the free bus ticket twice (one to get to the main site on Friday/Saturday and one to get you back on the Sunday)

****PLEASE BEAR IN MIND HOW LONG ALL OF THIS WILL TAKE. AT THE MOMENT ALMOST ALL OF YOU ARE ARRIVING ON SATURDAY SO CANNOT AFFORD TO BE LATE. I estimate your journey from London train station to the campsite will take 2.15-2.30 hours, plus tent time, changing time and getting back to festival site. You're probably looking at 3.30 hours. And you might have to factor in getting your artist wristband before you're allowed on site.****

Seriously...just come camp on the Friday and make me feel less stressed 😋

Inside voice...soz guys, just foreseeing stress and disaster.

P.s. Friday night has Nancy Kerr, Will Pound (and me!)