For electric, make sure you buy an Induction motor mower. A while since I bought one now, but that ruled out all the cheap ones in the sheds, and you probably have to find a proper lawn mower stockist.
Induction motors are much better suited to grass cutting than the universal motors which things like flymos always used to have. You may find induction motor mowers are lower power rating for same cutting width, but you'll still get more cutting power, as they're matched to the task, whereas universal motors are exactly wrong for the task (but dirt cheap, and short lived, as rather more of the power goes into heating up the motor than cutting the lawn).