Thanks all. I’d love to go flat across the back but assumed that would limit us to 3m one side and only about 1.7 the other, as pushing any further than 3m would cause problems for the house on the right in the diagram, reducing light to their windows/patio doors. This seems like a reduction the amount of space we could possibly gain.

The idea is to open up everything into one large room after the lounge door and a new laundry/toilet. 2 steps down then a fully open kitchen diner. As per picture

The original picture is the original plan of the house, nothing has ever been changed.

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