I understand that the installation and annual sweeping of the chimney system should be carried out by certified personnel and insurance companies may well deny any claims relating to this not being done.
What I can’t find a simplay answer to is “Can a homeowner replace an old wood burner with a similar new one themselves without invalidating their home insurance?”
knowing how twitchy Insurers can be… and acknowledging that you will be changing the status quo under which you are currently insured… I reckon you should ask your current Insurers how they feel about it. 
EDIT: everything I check online says Installer “must be qualified”
That’s a good point.
I was already treating the “Do it yourself, it’ll be fine and they’ll never know.” advice with a pinch of salt the size of Belgium.
Guess I’m looking at quotes for supply and fitting now.
It wouldn’t stop me installing a new when needed. If any were to ask it was installed before the regs changed. That may shock some but as a competent engineer who observed the installation instructions I am not phased by it. Seen some pretty bad installations by HETAS engineers.
I talked to the chap who cleans the chimney each year for us about this sort of thing and he told me that legally I would have to replace the chimney liner as well when I replace the stove. Both have been in place for many years.
Yes that’s a good idea.