Two types of birds are most common in chimney problems, starlings but more often jackdaws (small crow with silver streak on its ears). From April till July (although problems often occur beyond these months, as jackdaws are very territorial and can hang about all year) it is the jackdaw nesting season.
You should never underestimate these birds as they are surprisingly intelligent and some of the most determined when it comes to procreation & nest building.
It is surprising how many cases of birds nests i see just driving around , all too often a bricked up fireplace hides a multitude of sins and takes the owner’s mind off the flue completely.
Unfortunately in the 1980’s many gas fire fitters ran amok fitting fires without ensuring the flues had been swept (and often without a proper GC1 or GC2 fitted on top of your chimney) so if you have a nest above your gas fire it is often the case a few bags of soot will come out too and you may still need the correct gas cap fitted.

What you need to consider when you have this problem

Firstly, so what exactly are you up against ?
The crows nests that can be seen in trees, are in this case; built on top of a structure akin to a beavers dam (which is often at least 6-10 ft deep or more) used to provide a support for the nest.
The worst case that i remember was an old big building in Barassie that had multiple generations of jackdaw nests on top of each other. The runs in the chimneys were convoluted hindering removal of the nest material and so the only course of action was to open up the wall above in the loft space.
We eventually removed 13 bin-bags of nesting material over a 9 hour period with little to no time for resting, removal is ALWAYS hard physical and labour intensive work.
To try to put a time figure on nest removal is kind of like asking how long is a piece of string, but on average with a wee bit of luck a nest takes between an hour to two hours to remove and will likely yield at least two or three bin bags full of stuff.

It gets worse too

If left unaddressed the worst case scenario for your house, is that it can and will eventually cause dampness problems that when severe enough will threaten your house.
Nests act as sponges for the rain which will eventually soak through into your inner and sometimes outer walls. Oftentimes, i will see the signs of dampness above the affected chimney fireplace where the walls meet the ceiling and this may be in the room directly above too, depending on the height of the nest and run of the flues.
If your building was built prior to the mid 1950’s then the mortar between your bricks/stones is made from sand and lime not concrete. This is very susceptible to the sulphurous acid made when the sulphur from coal soot is dissolved in rain coming into your chimney. If your flue gets damaged enough you will eventually need to get a liner fitted to be able to use it again, that’s rubble allowing of course.

What we can do for you

Firstly, we remind you that as long as there are eggs or chicks in the nest it is illegal to remove them unless you have a special license. So from April onwards you will need to wait till the birds have left (as you can read here RSPB Nest removal regulations.)
The most relevant parts are as follows, “The breeding season for Jackdaw’s is April – July. Therefore, if you are unsure there is a nesting Jackdaw, then the best advice is to wait until the end of August – September. Outwith April to July or if it is an old abandoned nest we will able to remove it completely for you.

We guarantee your birds nest problem will be removed completely as proven by our free CCTV inspection (minimum value £60) that you will be shown live at the time and your also chimney swept efficiently.

Please remember that this work can be messy because we need open access to the fireplace to create the forces necessary to remove the blockage. We cannot always close it to the same degree as when we are doing a normal sweeping job. So, you should consider covering your floors, furniture and perhaps removing things from the room in advance.

We charge minimum one hour inclusive (£100) and afterwards by the half hour so you only pay for exactly how long the job takes, no more no less.
We will remove all soot and nest materials efficiently and completely as shown by CCTV.
If we can do it in an hour or less it will be done because we do NOT mess around, or take breaks and we keep ourselves fit & strong for this purpose.
Supplying and fitting a bird cage is mandatory too because it is for your benefit… we simply don’t want to have to do the same job twice.