Assuming there is no noise at all from the unit, it’s possibly the thermostat, although the orange light being on indicates that “fast freeze” has been selected which would by-pass it.
Engineer time perhaps on this one I think, check repairs@ for one near you 😀
Thanks for the information, Dave – the amber light can be switched on or off with no effect. However, given high ‘call out’ charges is it worth taking a chance on the thermostat (which I can get for £22.99) and/or the ‘Defrost Stat & Fuse’ (which I can get from the same source for £18.99).