Also, you will have checked the MCB protecting the circuit that feeds the socket outlet which you were using; and checked the mower’s plug itself and the mower’s own protective cut out.

If it’s none of these then you may have damaged the lawn mower’s blade bearing when the wire got trapped. Have a look and see if there is a piece of wire insulation trapped behind the blade. This would prevent the motor turning and cause it to trip-out whenever you power-up. This will possibly mean a strip-down, depending on the design of the machine.