hmmm shall watch this topic developing...
I can't be of much help regarding the organisation of a festival IN THE UK... however I would say you make a rough sketch and visit local authorities (in the best garment available).
Generally you will have to keep up with a huge pile of work, starting by collecting informations on (costs of)
- space
- schedule
- (local) licenses
- team
- insurance
- power supply
- amenities
- food
- security
- waste management
- parking
- volunteers
- promotion
- funds/ costs
- sponsors
best is to visit a successful festival and run around with open eyes - maybe even ask questions

Timing and space are essential for a successful event. If your event is in the same slot with other huge (established) venues, you may not get anyone. If your location is remote, it will be underground and only the dedicated will come - which can be attractive in its own way.
You need to check with local authorities, as to find out what their requirements are. Wear your best garment and ideally you do not to show up alone.
Make a checklist and definitely ask for the timeline they need for processing your request.
Gather a team of 3 or 4 people who help you organize. Any number >4 will be a mess. There should not be more than these managing the event, each and every with sub-divisions. One responsible for overall management/ licenses/ finances/ infrastructure, one responsible for stage area, one responsible for food and stalls, one for camping... the more you centralize the topics, the more work it will be but you will have small meetings - saving time and nerves. Each and every manager then has a small team her/ himself to gather and to make meetings with.
Insurance is important in the West, so look up the white pages or goole for companies.
As previously said, you might need a generator that you can rent (they are way not as costly as they have been in the past - BUT they run on petrol/ diesel - make a calculation (worst case scenario))
How many people, how many days? You definitely need toilets... 50 ppl can share one... Cleaning team for the toilets (an all-time favorite) and count at least one more in case another breaks down... some rental companies will provide you with emergency backup and cleaning teams during the event.
Food is important, choose simple food that can be stored and will last a few hours without a fridge. Choose a good ratio as in price-value... Use recyclable plates and cups whenever possible.
Security as mentioned above. Count less in the beginning (first days) and more in the end... never be understaffed, rather have one sitting around, doing nothing and being available when the crap hits the fan.
Waste management is very important, you need to clarify where you can dump the stuff and who is going to help you.
Organize parking space and count generously. People share rides and come with trains and busses, but think of a shuttle bus. Good parking organisation will keep the locals calm.
You n.e.e.d volunteers - and there are so beautiful people out there who are willing to sacrifice for a good cause... I would not have made the InJuCo without volunteers... the first event I ran almost all by myself, on the second I had a team of 10 people assisting me... without them, the convention would not have happened. Next time YOU go to a festival - volunteer and learn. I did on the EJC and really: it has been great fun and a learning experience.
How will you promote your event? Flyers are essential, unless your event is established... The EJC really does not need any adverts - but it needs a website. Be aware that ppl are only believing what they see...
Generously calculate your costs - always be ready to spend 10 - 20% more than calculated.
And if you don't have the funds, look for sponsors - offer them "exposure"

Last
Most important of all remember that you're doing it because you love it!!
Be ready to
Sacrifice, to have NO fun on your event and to be

pit digger, medic, counsellor, electrician, driver, MC, entertainer, etc all in one person, not atttending a single workshop and maybe even missing out on the (gala) shows... and in the end - with nobody standing by - be ready to even go to jail for it.
