Maximum wattage heater for safe use of 10amp circuitry
I have a few appliances (like the kettle) that I use in my house that have heating elements/power consumption rated at 2400W, which I believe is the maximum that I should run in a standard 10amp power plug.
Is 2400W safe for constant use in a 10 amp circuit or would it be best to run slightly less power-hungry devices in order to add a margin of safety?
yes it is, technically speaking the cabling on a power circuit should handle the breaker size (after all the breaker is there to protect the wiring).
as you alluded the weakest link is the flexible cable to the device, most run .5/.75 and 1.0 mm^2 the current carrying capacities of these vary with the insulation (V75/V90 etc..) and the run, the rating assume unenclosed in air so make sure you don't do anything like run the cable under carpet/mats for example so the cable can adequately dissipate the heat.