Hi Carly,
I'm an Essex type myself.
I think that Friern Manor in Dunton do 'party nights' where a group of you can go along and they organise games and bitzas, however it wont just be you and your party there - there will be lots of others around too.
What about something like one of the rooms in the Orsett Hall or even the Thurrock hotel.
They'll both provide a lovely dinner in a private room and you can just prepare the games yourself.
My final hit in my area would be the Moathouse just off the A13 which has function rooms where you can arrange a dinner.
Good luck!

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Saturday 16th June 2001 - St Catherine's Church,
Some people are like slinkies, not really good for anything, but they bring a smile to your face when pushed down the stairs