Mate looked into doing his house.
Chimney had been prepped and lined a few years before he bought the house.
Was told it didn't meet current building regs and thus relining was a requirement of the company doing the fitting, and the lining's have a service life anyway.
Mate didn't buy a woodburner.
I have 2 open fireplaces. I made a cover plate from 3mm plate steel for the opening, and have a short length of pipe going through and up the chimney. Easy to pull apart for cleaning, also got a gizmo to check for dangerous gases. Only a small burner.
As i understand things, to install by a fitter a woodburner it must meet all requirements of building regs. If you die in your sleep, any surviving family members can sue the fitters. So a fitter will follow the rules and building regs to the letter. Like only Corgi plumbers can fit gas boilers.
If you do it yourself, and everything checks out, go nuts, self install. You might have to remove it if you sell the property as you won't have official paperwork to say it's fitted in accordance with building regs.
I did it myself. If i ever sell my place i would have to remove the woodburner before sale. If the new owners wanted it, and fitted it back themselves then thats for them to arrange.