From a building regulations point of view, it *may* not be required to
line the chimney - if putting it back into use is considered a
repair.

If OTOH it's regarded as disused, building regs would I think apply.

However there's several reasons why it's a good idea to line
regardless.

Stainless steel liners for solid fuel are far from cheap - think about
costs being similar to a good quality stove (also don't be misled by
the price for linings for gas boilers - they're much cheaper but
unsuitable for solid fuel).

However if you're having the chimney stack rebuilt, that's the ideal
time to have a liner put in. It isn't unusual to have to at least have
to take the pot off anyway, and often the flaunching requires repair.

Other important stuff is the chimney is well designed to draw well and
avoid downdraughts - which depends on a myriad of things, surrounding
terrain/buildings/trees, shape of your roof, height of chimney above
roof - some of which may have changed since the original build.

A liner helps the stove to draw well, which reduces sooting and
improves rapid heat-up (reducing the chances and consequences of a
chimney fire - which can be bloody scary) - and in some cases may be
important for safety.

Ideally you want to get a look at the state of the masonry inside the
chimney. The combination of many years of usage/sooting along with
rainwater can lead to considerable mortar erosion - in which case
definitely don't skip the liner.

If the chimney is significantly larger than the liner, filling the
space between with vermiculite is common practice.

Take Christmas as an opportunity to stuff smaller relatives up the
chimney for closer inspection.

Much good advice in Part J of the building regs:

http://www.planningportal.gov.uk/eng...documentslist/