My front door has no threshold support (Ed.)

[threedee]

We recently moved into this house and still discovering corner cutting in building quality. House is built in 1999/2000.

So, i decided to replace my 25 year old front door (upvc) to composite.
Surveyor comes in to measure up and upon lifting top step of entrance we discover my current door hanging in midair not resting on anything.
There's a gap of 10 mm between badly placed, too small of a block in the middle, effectively making a levitating door with bendy threshold on a bottom frame.
Also voids on both sides under floor so long i can stick my hand in there, there is NO support at the bottom at all...

I need ideas how to fix this without wrecking the place...

Wasnt there supposed to be some sort of threshold block there ?

 

[freddiemercurystwin]

@crank39
@ronniecabers

 

[johnny2007]

You have to ask the person who will fit your composite door.
Then you won't have any issue.
But obviously I would like to see my front door frame supported at the bottom.

 

[Alec_t]

I need ideas how to fix this without wrecking the place..

Shove 10mm of slate/tile under the threshold?

 

[Diver Fred]

I think that the bricks that formed the step need to be removed, maybe even the slabs lifted to see what is at the back of the step. Houses built then should have wheelchair access as standard (i.e. no step at the threshold).
What are your neighbours doorways like? Similar or different? Where is the DPC?