From a quick look there are only two trainers in Essex right now. One on the border at E Bergholt & the other near Bishop Stortford. When I first looked into ringing 6 years ago, there was only one. s
I found many more ringers when I moved to Suffolk and was lucky enough to be taken on board by a group who ring near me. There are 5-6 willing to take on trainees in Suffolk including one person who I train with who is part of our group & already has 1 other trainee. We have two trainers in our group, as well as 2 A permit holders, and you can also be supervised by A permit holders within a larger group.
See a map to find trainers in your area:
http://blx1.bto.org/ringingTrainers/ringing-trainers.jsp?ref=TM34
I started off many years ago observing and helping in Japan. When I came back to the UK I attended a course for beginners run by the BTO at the Field Studies Centre at Flatford. A bit pricey, but a great introduction & well worth it. See courses here:
http://www.bto.org/volunteer-surveys/ringing/taking-part/training-courses
It can be hard work erecting nets, lane-clearing and carrying equipment, as well as early mornings, but what you can learn in terms of the birds themselves, the skill of extraction and potentially adding a little to everyone's knowledge on birds makes it worthwhile.
Depending on how much free time and money you have, it can take a long time to achieve your 'C' permit.
Sean