Trigger,
The visit may be from what the DWP calls a Customer Compliance Officer.
It's not uncommon for them to visit people in their own home - for example, if someone has missed sending in a required form, missed an appointment, or if someone else has reported 'something' to the DWP. They also often make entirely random visits to people in receipt of certain benefits - so as to check that benefits are not being claimed fraudulently, or alternatively to carry out a 'benefits review' to make sure that someone is claiming all the benefits they should/could claim. They often call people into the office - but with people in receipt of disability benefits, the visit would take place in the home.
If you have nothing to hide, you have nothing to worry about. It may not be in connection with your application for AA at all - it could be purely coincidental. Do post back here once you know more about the visit.