Hi Dave
I know the feeling it sucks that sadly is the nature of the security game i would check things out with some situations they have to give you a certain amount of notice before they change pre set shifts.
I had a simular situation over here during the summer.
I was working doing some security at a very very high end Hotel the boss as he liked to call himself was an a-----le he had no Police Military background, mind you he had degrees coming out of every orifice.
I had leave booked for when my kids were coming over.
The afternoon i was picking my kids up from the airport he contacted me and told me that it was all changed and i would have to come to work that night and that my complete shift situation had changed basicaly for the whole period of time that my son were in the US,i had not seen my two boys for 6months.
He explained that HE had to attend some courses so he would require me to work extra shifts and he had adjusted the rota . and that i would be in charge..yahoo!!!.
I met him in work that night and got him to the front area of the Hotel reception i asked him why, and he said it would look good on my resume.
With that i asked him to look around the reception area of the hotel and in front of some very high end guests said
'if you think for one moment that i would choose between my kids and this job you are wrong".
Walked up to reception with him saying you cant do this handed my radio my keys and my id over to the front of house manager and said ..Oh yes i bloody can enjoy your stay..you might have to do some work.
And the drive home was wonderful dont do that Dave i had plenty of work but it felt bloody great.
Cheers Chris