The short answer is no. There is an appeals process for planning applications that have been refused, but not for objectors when the application is approved against their desires.
Loss of light: impossible to know for sure, but the general rule that planning departments operate to is one of the 45 degree rule (at the side) in respect of overlooking of new windows on the first floor of the extension into the garden of the existing property, and wrt. the appearance of the new extension from the viewline of the existing windows in neighbours houses (habitable room windows only). I'm afraid if you believe that loss of light into the GARDEN is a planning consideration, you are misinformed.
'Extension will clearly be visible from the road which is 50m away'. Are you serious? Green Belt or not, an extension which is 50m away from the road is never going to be a winner as the reason for objection.
'Set to lose views' Another misapprehension, I'm afraid. A right to a view of a neighbour, per se, is never a planning consideration. Only in the context of the bulk/mass of the proposed dwelling in relation to what surrounds it is it a consideration.