I happened to spot last night that the Labour manifesto promises that no 5-, 6- or 7-year old child will be taught in a class of more than 30. Assuming they really mean exactly what they say and don't intend to drop this promise if they get into power, it has some consequences.
Since Y3 includes 7-year olds, it means that the class size limit will be extended to Y3. If taken literally, it also means that any mixed year class (Y3/4, say) will be subject to the class size limit.
At the moment KS1 classes can only go over 30 if a child is admitted on appeal or via the FAP. It may be that Labour plan to provide an additional teacher and a portakabin in these situations. If not, the only way they can deliver this is to remove the concept of excepted children completely and make ICS appeals unwinnable. So, even if you missed out due to a mistake by the admission authority, your child won't get a place. And if you have a young child and move into an area where the nearest school with places is 30 miles away, that is the round trip you will face every day.
If Labour win the election I would strongly recommend lobbying the new Education Secretary to make sure this proposal is abandoned.