Thanks you lot.
I have spokedn to head of MFL who is organising trip, although the slips were handed into the finance office.
9 and 10 were her best friends, so I can easily speak to those parents.
Mrs A was agreed with me that FCFS was not the ideal system, but had always worked out ok in previous years. 
To give a bt more info - the pupils visit one of 3 European countries next June - 35 to each country - there are 4 MFLs at the school - thse doing Japanese are guaranteed to go to a certain country (their second MFL), leaving 10 places open for the other pupils. The reason I would really like DD2 to go to this country - this is the language that she'd like to do to GCSE, this is the country DD1 went to (as one of the predetermined places, so I haven't experienced this before) and I would like them to have the same opportunities. Also, the city which she would be visiting as her second choice, is where we spent our annual holiday a month ago, so she's already had that experience, iyswim.
Mrs A understood my concerns and said she's investigate on Tuesday which is the cut-off point for the slips to be handed in and review it then. She also said that as the system was advertised as a FCFS it would be difficult to alter this, although sje would consider a different system in future.
I then felt I had to point out the child handing in3 slips, which she agreed was unaccpetable. But did not really clarify how this would be addressed. I said that the fact that a pupil was handing in for other children emphasised the unfairness of the system, as perhaps they had other commitments in school/travel arrangements etc.
I don't think Mrs A knows I am a governor, and I certainly didn't mention it - I will address this as a parent, but I am determined to raise this at the next meeting as a process that may need reconsidering - particularly from the potential discriminatory POV.
Thanks again, everyone.