In every major incident the mobile network is the first thing to fail — not from damage, but from everybody calling at once. This works out what you can actually reach with, how far a handheld radio will really carry, how long your batteries last, and a check-in plan that still works when the phones are down.
VHF and UHF radio travels in straight lines and is stopped by the curve of the earth and by anything solid. The manufacturer's "up to 10 km" on a handheld packet is measured on a mountaintop with nothing in the way. In a town at street level, with buildings and trees, a 0.5 W PMR446 handheld will typically manage a few hundred metres to about 2 km. That is not a fault; it is the same for every brand.
Height is the only thing that changes this meaningfully. Doubling your antenna height increases your radio horizon by about 40%, and it costs nothing. Getting to the top floor of a building, a hill, or simply holding the radio away from your body and out of a vehicle will outperform any amount of extra power.
In the UK, PMR446 is licence-free: 16 channels at 0.5 W ERP on 446 MHz, and a growing number of digital (dPMR/DMR) channels. It is legal for anyone to use. Marine VHF channel 16 is the international distress and calling channel and is monitored continuously โ if you are in genuine danger on the water and have a handheld, that is the channel. Amateur radio needs a licence but is the only hobby service with legal high-power and long-distance privileges, and amateur operators run emergency networks during real incidents.