Builder / architect question

Are you saying in between the coats and the cupboard is the space you want to open up?

 

It looks like there would be a lot of disruption and expense for what looks less than 1m2 of additional floorspace (appears to be only about 900 x 700mm). If an 'RSJ' (correct term these days is Universal Beam) has been used it probably only extends part way into the cavity wall at the end to be extended and a site welded, plated, bolted connection to a UB stub extension projecting into a new cavity wall squaring off the corner might be possible, but I would class that as a question for a Structural Engineer, rather than Architect/Builder.

There could be a lot more work involved if a steel/concrete lintel has been used. When was it extended and would your local Building Control (perhaps too small for Planning?) department still have records. Perhaps these were requested by your Conveyancer when you purchased?

What's externally in the corner to extended over? (manhole, underground drainage, etc., as there could be a reason why that oringinal extension never went full length).

(Is that pitched ceiling to avoid the inelegant appearance of some extensions that have the pitched roof above extending almost right up to the underside of bedroom window cills above?

 

One big difference I've noticed between kitchens here and over the water is that we do not put laundering equipment in ours. We have it in a separate room or the cellar. I think that not having the kitchen function as anything but a kitchen usually results in more storage. It's interesting to see these differences.