The comparison is the point
An inventory on its own proves very little. An inventory compared against a check-out on the same structure, item by item, is what turns "the carpet is ruined" into a specific, dated, evidenced difference.
Templates
There are ready-made room templates covering the usual UK property types, so you are ticking and photographing rather than inventing a structure at the door.
Which check-in gets used
The one from the start of the tenancy you are ending, not the most recent one on the property. That distinction matters on a re-let and it is handled for you.
If you would rather not do it yourself
An inventory visit is one of the services you can book, and it is the one most worth handing over, because a rushed inventory is worse than none: it looks like evidence until it is examined.