Yes they can.
LEDs are diodes and only allow power to pass in one direction – they must be powered from a DC source that limits the current flowing through them. If LEDs are connected directly to the UK 230v AC mains supply without any current limiting LED driver or LED power supply they will most likely fail immediately and catastrophically with possible damage to the fixture.
If LEDs are powered via an LED driver or Power Supply that supplies an incorrect voltage several outcomes are possible. If the current and/or voltage is too low the LEDs will appear too dim or fail to light. If the current and /or voltage is too high the LEDs could age prematurely (in the case of minor overdrive) or at the other extreme fail catastrophically.