Posted: 01/04/2014 at 15:52
You can cut it back now, but you will have to check for nesting birds as disturbing them is a criminal offence.
There is also the probability of overwintering insect, particularly butterflies. If I were you I'd trim the top now to a manageable level, then in about July when most of the chicks have fledged and before some insects have laid their eggs.
You can't please all the wildlife so some will suffer, but leaving it a bit later will allow the ivy to recover and some food and laying opportunities for insects.