Standardizing Postcodes

I have a file of 60000 postcodes, which I've created a page to sum up certain ranges that we're interested in.

The postcodes should all be in the format AA11 1AA, but the people entering in the info are not very conistant. Is there anyway I can have a macro check column B for each cell to ensure that it's in the format AA11 1AA, and where its been entered as AA111AA, add the missing space?

*edit*
I forgot about postcodes like A11 instead of AA11, and AA1 instead of AA11. The space therefore needs to be inserted 3 from the right, if their isnt one already. Any other spaces in the cell might as well be deleted while we're at it!