I am applying to Henrietta Barnet for my daughter but have been told by her current headteacher that if I don't put our local high school as first choice, as it is a popular school, she will not be offered a place there. I would want this school to be back up in case she does not get in to HB. On the other hand I am worried that if I put HB down as second choice, she won't be offered a place there even if she does achieve top marks in the tests as the guidance books say that if there are 2 offers, she will only be offered a place at the school which was ranked as higher preference on the application form. I would be really grateful if anyone could help clarify this?
You (and mad and hermanmunster) are right and the headteacher is wrong, possibly because the rules changed last year and he/she may be out of date.
Each admission authority (VA school, foundation school or LEA) is sent a list of applicants who have named that school on their CAF. They are not told where you ranked them. They then apply their criteria and produce a list of those to whom they wish to offer a place at the school, which are sent to your home LEA. The LEA looks for people with more than one offer, and tells the lower ranked schools to re-allocate the place. This continues until there is no movement. (In practice the admissions authorities send a ranked list for each of their criteria, but the effect is the same.)
So if you rank HB first and the local school second and if both accept you, your final offer will be HB and the place at the local school will be allocated to someone else. If only one of them offers you a place, that will be your offer. Or to put it another way, if you meet the criteria for the local school, your offer there will be withdrawn only if you have an offer from a higher-ranked school.