Can I sense-check my plan for school admission with you?

[HerculesMulligan]

DS starts primary school in SW London next Sept (2018) so we're in the application window now.

We currently live in House A, and have done for 5 years. It is practically in the playground of DesiredSchool and so DS' admission is as certain as it's possible to be.

Timings have conspired so we are in the process of trying to buy House B, and are not sure yet whether we'll be in by the end of Jan. We think we should be, but we haven't exchanged yet.

House B would have been close enough to DesiredSchool in the past three years for us to get DS into Reception. (It's a faith school but we score well on that criteria). Moving slightly further away from the school is a risk, we know, but it's the right house for us and they don't often come up, so we think we have to do it, rather than waiting to move until after September.

I presume the right thing to do is to wait as long as we can without missing the 15 Jan deadline and then apply from whichever house we're in at that moment? Rather than applying from House A now and then notifying them of House B at some point pre-/post-January 15th?

I'm not especially worried about admissions from either house. What really worries me is the potential for misunderstanding - we are definitely not gaming the system (we're heading in the wrong direction for one thing), just moving at an awkward time of year.

Apply for the school putting the address of the house you are in at the time of filling the form in from your laptop. :)

Apply from where you live at the time of application.

In London you'll be using the online eAdmissions service. You can log in and amend your details/application even after you've submitted it, right up until midnight on deadline day.

So apply at any time, and change your details if you need to nearer the time.

You are correct, leave it as long as possible and push like crazy to have completed and moved in by January 15th, so you can use address B.
If not in by the cut off date, then use address A. Most LAs have a subsequent cut off date for just such a situation as you when moving a house which allows you to change your address but still be counted as an on-time application.
The one thing to avoid is getting into a situation of changing address and the LA assuming it is a late application. If the address changes between Jan15th and April date of release of school places (and assuming that there is not capacity to change address and still be counted as on-time) then you need to inform the LA but state in writing that it is for communication purposes only, that you need them to use address A as the address for admission purposes.