If you don't get in any school, can you choose among the undersubscribed ones or must you accept what the council chooses for you?

You need to check and compare the admissions policy for each school. Please don’t rely on the general consensus here. Each school can set there admissions policy how the see fit. Generally speaking looked after children are given first priority in our whole county but the rest vary greatly between schools. One local school puts catchment area as the 2nd criteria another has distance to the school as 5th and prioritises things like siblings, SEN & medical needs. Check each of your schools and work out where you’ll stand in each one.

@DawsonsGeek is right, but there is of course a risk that your favourite of the nearby undersubscribed schools ends up full this year (assuming you are planning an application for the autumn rather than you have made one and are trying to switch now - ?)

Undersubscribed state schools (except for grammar schools) have to accept any student who applies for a place, so you can choose. This is based on the School Admissions Code so it's applicable for all maintained schools in England. What will vary by school and LA is the specific process for applying for a school at this stage, but you should be able to find that on each school's website or the borough's school admissions site.

ETA: If the school is undersubscribed now (they haven't offered up to their PAN) you don't need to wait, you can go ahead and submit an application. Schools cannot hold empty places just in case a higher-priority applicant comes along later.

Yes. If you don’t get into any of your six choices in London then you will be allocated your closest school with an available place on offer day. But you can then fill in an ST2 form immediately, naming your preferred undersubscribed school and, provided there are still places, you will be allocated it within a few weeks, well before your child actually starts school. The form will be available on your local authority’s website under the school admissions section.

Sorry, no, but I would imagine schools do want places filled. There is a lot of movement early September as well once they start. If people can apply for schools out of catchment I can't see why it would be a problem?

yes contact the school you want now. Confirm they have space for starting Sept, tell them you want your kid to go there but they’ve been allocated another school and ask their process. They might tell you to contact the Council, they might be more helpful - that definitely does vary school to school! All schools want all their places full - they get funded per child. Each child is money to them really and they don’t want to be undersubscribed as that means less funding. It’s the same across England for state schools, can’t comment other countries.

Can only comment on rules in leicester(shire). Friend was given a list of schools to apply to that had spaces in the county. I said try undersubscribed ones in leicester city and she contacted one directly and went to look around (would have had to go via the online portal once she knew there was a place). Got her son into one she preferred.

If you know a school is undersubscribed and therefore has places available to start September then you can choose to go there. I’d contact the school to confirm the place and ask the process and same to the local Council. There should be nothing to stop you moving to any school that has space.