I'm quite new to regex and very much stuck with the following expression. I'm looking for a regex code that allows the following combinations: 

```
AA1A 1AA
AA 12
A 12
A 1

```

Requirements:

* String can not start with a number
* Only capital letters (A-Z)
* 1 space is required at predetermined places (see above examples)
* Numbers 0-9 can be used

I am currently working on/with the following string 

`([A-Z]{1,2}|[A-Z0-9]{1,4})([ ]{1})([0-9A-Z]{1,3})`

The issue with this one that it does not allow the `AA1A 1AA` string.. 

Any ideas?