This was hidden!!!!!! I found it by accident - under the carpet - by poking a finger - sheer luck I found it!!!!!! Otherwise it would have wrecked the sill but I found it in time!

And that was yesterday!

£12 of welding later!!!!!:

Now you see it...

...now you don't !

thats the inside, what about the sill underneath??
as i assume it has rusted from outside in?

Nope! inside out!
outer sill was solid as!
I know - tapped away at it right proper!
All the rust was cut right out
BUT!!!! The rubber door seals were a surprising source of rust as the METAL SILL CLAMPS (at each end of the rubber seal - they meet at the bottom - ) were really rusty and they were running down into the sill!!!!

The rubber door seals, where they meet, is a favourite rust spot. I always remove them and move the join to half way up the door frame so the water can't gather at the bottom and cause rust.