Complex sentence: Under British law, anyone arrested in England, Wales or Northern Ireland has their DNA profile taken and stored on the database whether or not they are convicted (different rules apply in Scotland), which now contains the DNA information of nearly five million people.
Split into simpler sentences: Under British law, anyone arrested in England, Wales or Northern Ireland has their DNA profile taken and stored on the database whether or not they are convicted (different rules apply in Scotland). The national database now contains the DNA information of nearly five million people.