newbie - Spreadbetting after hours


hello, i am looking into the possibilties of spreadbetting the daily ftse. I have noticed that you can trade it after hours, I have seen some companies quoting that they trade up till 9 - 10pm. I would like to know if the closing price for the ftse at the end of the day is the price you can trade on after hours or can the spread betters offer you any price they want to?

I have often done a trade on the Dow or Dax after hours.. even at 23:00!
FTSE prices track the US indices after 4:30pm but they don't move much after the US markets close. I have been able to run FTSE catch-up trades out of hours, where the FTSE has closed in the opposite direction to the US, and then catches up (often over-reacting as it does) just before and just after the London opening the following morning. Its been succesful more often than not for me, sometimes I have even hit my target and got out before London opens, but the big gains come from longer holding periods.