Removing Chimney

[Firsttimebuyer2020]

We're going to rip out or gas fire and can't decide whether to remove the chimney or not. It's not on a party wall. It runs through the middle of the house. Removing the chimney breast would create much needed space on the ground floor and create more wall space in a bedroom. As you can tell from the user name I am a complete beginner and have no idea how much work/cost we're looking at.

You will have to follow building regulations, get a builder in for a quote

It could be structural or at least adding to the strength of the building.

If you ever go to remote places for a walk and come across old ruined buildings it is quite often the chimney stack that is still standing.

Removing a chimney is heavy and filthy work. You also can't just remove the bottom bit of a chimney without making sure the whole upper structure is properly supported.
We had an entire chimney removed, top to bottom of house. I can't tell you the cost as it was included in loads of other work, but I can tell you it rendered all the rooms with a chimney in them unusable for the duration of the work. There was dust and soot floating around, even in the attic, where they had to remove the top bit of the chimney and make good the roof.
It's really a job for an experienced builder.

Removing chimney breasts can create a lot of space, but can also affect the wider structure of the building (and I should know, having just paid out the best part of £20k to fix bulging walls relating in part to chimney breasts being removed before I lived here). At the very least, get some proper advice from a qualified structural engineer (not just a builder).
I personally have had my fingers burned and wouldn't do it.

I have just removed a whole chimney stack in order to knock two rooms together on the ground floor. Yes it’s released a lot of space, but it has been costly (15k for all building work, steel work, and making good - though it seems like you might want to leave the wall in tact so that might reduce a bit). It has also been horrifically messy - 100 year old soot and brick dust everywhere. For us, it is worth it for the layout change, but we went into it with our eyes open and it’s still a bit of a nightmare. And will have taken 2 months from start to finish of new kitchen. You can’t do anything without speaking to a structural engineer!

I'd leave the chimney breast intact for structural reasons - and it is a VERY messy long winded job - seriously you don't want to go there unless you have to - especially with a semi-detached building.
One option is to just take out the fireplace and leave the rest. I've done this is in three houses I've owned. Once you've taken out the fireplace (and all the backfill around) it creates a surprisingly large space. In the first house I did it in the fireplace was in the kitchen and the space was big enough to put the fridge and freezer into. In the second I made the spaces into cupboards.

To add that just removing the fireplace is not difficult. A day's work at most - though where you put a ton of building rubble might be a bit of a problem - and it's a job well within the skillset of the average Joe. Just don't get too enthusiastic and take away the relieving arch, or lintel, holding the rest of the breast up. (Even if you do, the house isn't going to fall down on you - unless you've got a really crappily built house - and replacing it is easy.)

www.diy-extra.co.uk/removing-a-fireplace.html

We've just had the chimney removed in the 2 house rooms but left it in the loft/roof so we can attach our Sky dish to it!

Cost was £4325 including making good everything. Would have been cheaper to remove all of it but due to neighbour's trees the chimney is the only way to get Sky! It took 5 working days. Made a hell of a mess but so worth it!