Please can you advise me on whether or not by law or for insurance purposes, I need to install a certain type of fire alarm in certain positions in a recently purchased house which has been recently changed with some rewiring. I am wanting to install alarms upstairs and downstairs and in the garage.
Thank you.

 

Any decent electrician should have included the appropriate detection as part of the rewire.

Existing owner occupied houses aren't required to have anything, but a Grade D LD3 system is recommended minimum with hard wired detectors (i.e. powered by 240V) that have an internal back up power source linked to each other by cable or wireless bases (so they all go off) located in circulation areas. Smoke detection to escape routes, heat to the garage (false alarm risk)

All available on the Safelincs site

It would be up to the insurance company what they require (if anything)  It is not law that you have to have smoke alarms in an unaltered house (But it is a very good idea that you do)

A house that has had just a rewire does not have to have smoke alarms fitted, but as said previously it is a good idea.

Smoke alarms  have to be installed under building regulations if the house has had another another level installed, a loft conversion to a habitable area or any new habitable area above ground level.

 

 

A point worth mentioning, when was the house constructed, if it was after 1991 then the Smoke Detectors Act 1991 applies. Check out http://www.legislation.gov.uk/ukpga/1991/37/contents .

And smoke alarms have been a Building Regulations requirement for many years also (leading to the Smoke Detectors Act being finally repealed in 2006)

AB I stand corrected but would BR apply for a rewire?

Not necessarily (although I've been told in the past that a replacement fire alarm system technically needs BR approval, but no one bothers) although the OP mentions other alterations that could have led to it applying