Finding out more about catchment areas

[Marvellous]

We're househunting at the moment - no children yet but that's the next plan and we understand that school admissions are cut-throat here. Most of the nearby schools are great but we imagine we'd prefer the local Catholic primary as we've been active parishioners for several years already. I realise that this may betray me as a serious control freak (ahem) and acknowledge there's no way of telling how such things might work in 5+ years' time, but it would feel insane to spend more money than we ever have before without first doing a bit of research about this. How do we find out more about this? Is it even possible?

Catholic primary schools tend not to have catchment areas, though they often use the church boundaries within their admission criteria.
It is not the catchment zone you need to concentrate on but the admission criteria used by the school. TYpically in a catholic school this will give priority to children who are baptised and whose parents are regular attenders at specified churchs before any distance criteria. So if you are active parishioners and can meet these criteria you have a better chance of success, though obviously the nearer the school you are the better it is also.
You can find data for the previous years admissions in terms of how many applications and under what criteria the last place for the school was offered in a booklet which is published by every Local Authority. The primary one will be out in the next couple of weeks and you can look on the web for it or get a hard copy from the LA.
I would also suggest that you do consider the very long term considerations of which secondary school may be appropriate and just look at their admission criteria as well. A catholic school may well give priority to specified primary schools, whereas a maintained school could be more about distance.

Thanks - that's really helpful. The admission criteria are on the school's website so that should be easy to check.

I'm in Richmond upon Thames, which doesn't have an RC secondary school at the moment but may have one fairly soon. I felt fairly comfortable with a non-denom secondary before the recent discussions about a Catholic secondary began, so the situation's only likely to stay the same or improve.

As a simple rule of thumb following my shenanigans last year:

Work out education to age 11, consider any grammar initiatives, make sure you totally 100% understand the rules on catchment and religious variances, watch out for feeder school status, look into Academy applications and mergers to make feeder school status, etc.

Then move to well within the boundaries you need, renting if necessary (not applicable in your case) and be prepared to move again when they are around 9/10 years old at the latest (earlier if possible) to secure the same for secondary education.

You will get slated from those who will not / cannot / are to lazy to move but hey, it is your child, not theirs who you are concerned about.