Why not Scotland?

OK, so the site is called "Crime Check UK", but it only covers England and Wales. Why is that?

Simply, because policing is a devolved matter, and that includes the publication of data. Police Scotland doesn't have an equivalent of the data downloads and API published for the rest of the UK. There is some data available, and including it here in some form is on the to do list, but it's unlikely to happen soon.

And why not Northern Ireland either?

In this case, because, although the police data is available for Northern Ireland, the local authority data isn't available from Ordnance Survey and ONS - they only cover the mainland.

This isn't a problem we intend to try to work around. A lot of data that's freely available for Great Britain, such as local authority boundaries and even postcodes, isn't available for Northern Ireland (or, at least, isn't available under a licence which would permit its re-use here). If the Northern Ireland administration ever gets round to changing that, then we'll look at including NI police data, too. But, as it is, there's nothing we can do here with NI police data that isn't already done on the official police website, so we've got nothing useful we could add to it.