Don't quote me but I'd assume that it would be a months notice just the same as permanent employees as your rosters would run one month ahead and should you leave then arrangements would have to be made for your remaining work.
I also find it unlikely you will be dumped after 6 months, the likelyhood is that you will end up at LGW on midfleet. Which will be no bad thing, as I will be there to greet you! And I promise you it will be fun.
You could always ring BA and ask by the way.