What do they look for on bank statements for mortgage application?

[Fratelli]

Sorry to use aibu for this but it gets a lot of traffic!
We've got our decision in principle already so part of the next step is nationwide checking a few bank statements. What do they look for? We live within our means with no excessive spending but I just feel nervous about it!
Thanks

Checking that your outgoings and income are what you say they are. That you don't go into your overdraft more than you say you do etc. If your bank statements reflect what you told them then you have nothing to worry about.

Thank you, I've been nervous every time we've been in!