What’s this missing piece above entrance door?

velvetti

We moved into this house a few months ago but only noticed this gap in the ceiling outside our front door yesterday. The gap between the front cavity walls is not sealed and I can see through it all the way up when I stand outside my front door. Neighbour’s house has it blocked by a flat piece of wood or concrete (don’t know what material) as can be seen in one of the pics.
1) What’s the name of this missing item?
2) Does it need to be sealed urgently  and what problems could arise if not done quickly? 

Thanks

jonnydeppiwish!

A bit of soffit board to cover the gap?

molerat

Looks like it has moved for some reason.  Have you tried gently tapping it with a hammer to see if it will move to close the gap ?

itsthelittlethings

Isn’t it a lintel?

GrubbyGirl_2

Didn't your surveyor see that?  If not I'd ask him why and what his opinion is

RedFraggle

What does the full door look like? Were there once 2?