Birds nest underneath my bathroom loo!

Hi All

Due to the sudden increase in noise levels, it has become obvious a bird has nested and hatched her young under my loo! Its all built in but we have identified large holes in the outside wall around the waste pipe and a LOT of nesting material inside the unit and tiny little sounds coming from under the loo itself while we were looking around. 

I won't be disturbing it obviously, but once its clear I would like to block up the holes and provide a nesting box on the outside wall instead. 

Is there a reliable way to know when this would be safe as I need a plumber and a builder at the same time! I haven't seen the birds so don't know what type they are, intend to try and spot them this week but not sure I will!

Many thanks