What is the event Damo, how many will be there, are you representing the organisation and is it a serious event - would the organisation be at risk of losing funding if you made an a
rse of yourself ?
I'm guessing that they want you to speak of your own experience within the organisation and how its helped you get to where you are, in which case thats your speech written, stick to the brief, be brief but concise, give them your personal experience and not the company mission statement, the tip above about consciously slowing down is a good one, when you stand up to speak, pause, take a breath, smile at your audience, look confident and they will be put at ease, then start slowly...
Above all, write down what you are going to say, word for word not bullet points, write it all down, edit it, practice it, time it, edit in some pauses, be confident in the pauses, look around the room and speak to several random faces one-to-one, and remember, they don't hate you, they actually want to listen to your experiences and the council leader has probably just bored them to death so you could be the most interesting speaker they've heard all night.
And don't be afraid to just read straight from a sheet of paper, thats ok, you don't have to learn it off by heart, if you aren't that confident then just write it all down and read from the paper.
Don't try and be funny, it rarely works.