Essentially you require, from stove upwards:
Black vitreous pipe
Adaptor http://www.stovefitterswarehouse.co.uk/collections/twin-wall-flue/products/flex-to-twin-wall-adaptor connects liner to twin wall – this you have to site in the loft on top of your old stack. You may need to cap your old stack with a slab with a hole in the middle or a metal plate with a hole in the middle. The plate around the adaptor is 30cm square. Use Thunderbolts to screw it into your old stack.
Twin wall pipe out through roof lengths as required elbows if reqd. (2x elbows creating an offset can be useful as you can spin at the bottom joint amd “aim” the higher section between two rafters.
Narrow locking bands to secure twin wall items together