hand in the report/ hand the report in

Either is acceptable.

The verb to "hand in" is a phrasal verb. These are very common in English, and consist of a verb and another word or phrase. I was always taught not to split them.

1. We hand the report in.

Thus sentence (1) would have been judged informal and slangy by my teachers.

In the second example,

2. We hand in the report.

The phrasal verb is kept together. This is what I was taught to do. However native speakers do not always follow this rule, especially in conversation, and opinions differ about its validity

According to that view,

These are less preferable:

John folded the map up.
Peter put the fire out.
Mary cut the paper up.

These are more preferable:

John folded up the map.
Peter put out the fire.
Mary cut up the paper.

Many thanks, Contrex.

There is no rule in English that prevents certain phrasals from being split.

Thanks, JTT.

It is a matter of style preference only.

Thanks, Contrex.

Point noted.