Hi , you firstly need to have a chimney sweep check your chimney , with this you should expect to have the chimney swept professionally and a smoke test carried out , this will show the integrity of the flue/chimney . I would recommend you visit National Association of Chimney Sweeps website for a local qualified chimney sweep .
My answer is always dependant on the age, condition and size of the flue. So what do we mean by this?
In general, for a chimney to work satisfactory it must be
of adequate height and construction, of a size suitable for the appliance to which it is connected and most important, structurally sound. It is this last issue which causes most concern. The solid fuel association and building regs have always insisted a flue liner is only needed if the chimney is proven defective, especially if smoke and/or fumes are leaking into the property, or the chimney is oversize for the appliance.

Conversely there is an element within the trade who are wrongly advising customers it is NOW LAW that all chimneys must be lined, irrespective of the age and condition.
It’s no wonder people are confused.
I would recommend lining the chimney for a woodburning stove for 1 main reason regardless of condition of chimney .
1. For performance purposes . eg . 6inch outlet on stove will perform better with the right size of flue ie 6inch liner .( You may experience downdraught /blowback and a sluggish stove when trying to light it, if it is a larger chimney / flue ) .

I hope this helps .

Glen Shiell - The Stove Installation Company

You most certainly are going to need a stainless steel twin wall liner for your wood burner stove.
The liner you have at the moment for gas, is totally the wrong one for the wood burner.
These works come under building control, and need to be carried out by a Hetas registered installer, who will issue you a certificate upon completion.
You could do it yourself, but will need to inform building control, who will advise and check upon completion, plus you have to pay their fee.

as B J D says! dead right.