Note the blackening between the architrave and the ceiling, this indicates draughts are entering there, it should be caulked. The trap itself is dirty and there is a strong probability that it is not properly insulated and it is not sitting on its door stops again draughts are coming in there too, simple draught stripping will cure the problem but the top edge of the stops must be cleaned well first.
Airing cupboards often have gaps, cracks and holes round pipes, these should be sealed round ans simplest the way to do this is with acrylic caulk.
General advice on lofts:- They should be well ventilated, well insulated (in general the ceiling rafters should not be visible as insulation should be 300mm deep)
Like this :- not like this:-
In the following section we are highlighting some of the problems encountered at and above ceiling level in dry lined homes.
Ceiling roses should be inspected by unscrewing the rose and filling and sealing round the cable entry points is allowed with acrylic sealant. typically decorators caulk works fine.
Any other wires that pass through the ceiling should be sealed round too, possibly from above.
Then inspect any pipe boxings or soil pipe casing and ensure they are air sealed too.
Typically in dry lined homes there is a gap at the edge of a ceiling which leaves an open path for a lot of heat to escape from behind the plasterboard linings.
A simple fix