The official Groundspeak blurb for a mega reads;
Mega-Events are the ultimate gatherings for geocachers. Officially, events must surpass the 500 attendee mark to qualify for “Mega” status. Many Mega-Events are held annually, offer plenty of planned activities and attract geocachers from all over the world. Because of the international nature of these gatherings, Mega-Events are included in the Geocaching Weekly Newsletter, regardless of the distance of the event location from your home coordinates.
And so the 2015 UK Mega is coming to Essex, and specifically Billericay. A surprising choice of location at first glance as Billericay is your typical Essex town, encompassing all the thoughts that pop into your head when you are asked to imagine Essex. However, don’t let that put you off. Travelling a little further afield and you can discover a lot of the beautiful places that Essex has to offer. http://www.visitessex.com/what-to-do/ provides information on places to see and things to do if you are thinking of coming down, (or travelling up!) to the event. Please don’t assume that Billericay summerises all that the county has to offer!
The official site is http://www.mega2015.org.uk/