The choice of wired or wireless depends on specific circumstances.
In general, I prefer wired for reasons already listed.
If you already have a smaller wired system, it makes sense to try to extend what's already in place.
But it comes down to the practicalities of running the wiring into place.
If the void spaces are accessible, or the walls / ceiling are already opened for other works, then I'd always go with wired.
Even then, it may require a bit of access hatch cutting in plasterboard, but that's easily patched.
Other wall construction may be less easy to run wiring in.
If I was starting from scratch in an old building with poor access to run wiring, then I'd be tempted to go with wireless.
Some photos of my recent installation ( 4 x Smoke, 1 x Heat, 2 x CO ):
Alarums - running cables by
Ron Lowe, on Flickr
Alarums - installing bases by
Ron Lowe, on Flickr
Alarums - some making good required by
Ron Lowe, on Flickr
You've seen this one before:
Wago by
Ron Lowe, on Flickr
I still have scars on my heid where I whacked it off rafters and the like in the confined spaces, leading to blood everywhere.
In response to the BS stuff, yes, the detectors themselves must meet the relevant BS (eg BS EN14604:2005) as described in the Tolerable Standards doc.
https://www.gov.scot/publications/fire-and-smoke-alarms-tolerable-standard-guidance/The manufacturer's documentation will declare this.
The FireAngel units I used (SW1-PF, HW1-PF, CW1-PF) all meet the relevant BS.
In terms of the actual wiring, there's no Special Rules for the detector wiring.
It comes under the same rules as all the other wiring.
EDITED, to back-pedal slightly:
*Some* electrical work needs to be done under a Building Warrant.
This *does* require either someone who can self-certify, or a local authority building inspector to sign off on it.
You need to determine whether the proposed work requires a Building Warrant or not.
This may depend on the nature of the property.
If you are in doubt, then check with your own Local Authority on what work requires a warrant and what does not.
Here's one LA's take on it:
https://www.east-ayrshire.gov.uk/Resources/PDF/B/BSelectricalguidance.pdfPage 1 lists their requirements for a Mains Operated Fire Alarm system.
For my house, it does not.