Rough cost of london open plan and side return extension

We have a ground floor victorian terrace flat. We want to make our corridor, tiny kitchen and tiny dining room at the end of our flat into one room. That means knocking down two supporting walls, one of which includes a massive chimmney (around 1m wide by 50cm deep) and is around 3m long and the other is about 2m long. It would definitely need two steels which would form a T shape. Any idea how much this would roughly cost? We'd need a door put in, new floors and new kitchen (we are thinking ikea). Only looking for rough cost!!?? The other option is the same as above but with a 5ft side return extension (around 5.5m long) with glass in the roof and double patio doors at both ends (one to garden, one to courtyard as the side return can't go too far back or it will block off bedroom and bathroom windows). Ideally this would be all part of the same room above, or a separate narrow conservatory. Again, any rough idea of costs?? Desperate to know; thanks!!