Fire alarm fitters

Hello. Can anyone recommend a company that installs fire alarms? Our terraced Victorian house in Crouch End was converted to three flats in the 1970s. We have an old fire alarm system that dates from when one of the flats was used as offices, this has now been condemned due to wiring issues. We are therefore looking for a reputable fire alarm company to give us a quote as our freeholder has asked us to get recommendations to compare with their usual (and probably expensive) regular fire alarm servicing company. Has anyone got experience of this or able to recommend someone?

many thanks

chris