To be honest i think if we were going to have one, i would want a new liner anyway.
I guess nobody can know anything about a previous liner installed as nobody had anything to do with it (not any of us anyway).
And also i would expect a company to use a new one regardless as they surely wouldn't be able to guarantee a liner installed by any company other than themselves?
Absolutely correct. But, depending on the conditions previously outlined, and obviously making good thay area Ree pointed out, you may not need a liner. As a plan, and if there is any chance of a gas fire in the future, you may wish to consider having someone check out the position, when you have the existing set up removed. That way, you will know your options for the future. Hire a gasman dealing with gas fire installations. Have him remove the old kit, do flue smoke teste and inspect. Also consider the gas supply. If, say, it is lead, you may wish to have a rerun done. Or it may terminate in a position which will be imposibble to access later. Tell him upfront you are not planning to do it now, but you will pay for the disconnect and survey. (Some retailers may refuse, if there is no fire order. I would always do it, as it puts me in the frame for the eventual sale and work. But that's me) It will be a lot less hassle than when you have had the other work done, decorated and carpeted. For all you know, the chimney has been cut back and is beyond economical use. If there are no great issues, then have your initial work one in such a way that allows a relatively pain free installation later