smoker:
The biker is behind you, he is not going to hit me.
Oh, so I don’t need to indicate, if someone won’t hit me? 
It’s up to him to slow down. You don’t move just because someone else is going faster. Otherwise we’d all do 60 all the time. If you need to let him past, you pull in behind me !
No, I don’t move just because someone else is going faster. But I can make everyone’s lifes easier.
If you will indicate, I can change to lane 2, knowing, that before I reach you, you’ll pull to lane 1. If you won’t indicate, I can’t change lane, as it’s very likely, that you’ll stay on lane 2, and then, indeed, I will have to break sharply, as I would not be able to come back to lane 3 without smashing the motorbiker.
By that you can see, that if you don’t indicate, I have to take a risk of having to slow down to your speed if you stay on lane 2, or I just stay on my lane and the motorbiker will have to slow down. If you indicate, I will change lane to nale 2 knowing, that you will leave it soon and the motorbiker will can drive with his speed. It cost you nothing and it’s help us two, so what the point in NOT signalling?
Should a parked car indicate when you pass it because a bike comes up behind you ?
No, becouse parked car is not doing any maneuvres, unlike lorry driver, who’s changing lanes.
Once you move out from lane 1, you are responsible for your actions, not the people you are passing.
No Sorry, I meant, You are always responsible for your actions. Don’t try to pass the buck onto me !
Off course. I do not expect you to be responsible for MY actions. But I expect you to do YOUR ACTIONS properly. There is very well known British road rule “mirror signal maneuvre”. It’s not “mirror, signal (unless you think that it’s pointless), maneuvre”. So unless it’s really pointless, SIGNAL YOUR ACTIONS. If there is the smallest doubt if it’s pointless or not, you have to. And if there are some vehicles arround you, you can’t know if someone will need this indicating. And even if it’s not essential for me, but simply helpful, it’s not you to judge it. Your duty is to signal your maneuvres and that’s it. I may want to let the motorbiker pass or not. You MUST indicate, when changing lanes:
The Highway Code
Multi-lane carriageways (133-143)
Lane discipline
133
If you need to change lane, first use your mirrors and if necessary take a quick sideways glance to make sure you will not force another road user to change course or speed. When it is safe to do so, signal to indicate your intentions to other road users and when clear, move over.
There aren’t any exceptions here. It’s not written
“If you need to change lane, first use your mirrors and if necessary take a quick sideways glance to make sure you will not force another road user to change course or speed. When it is safe to do so, signal to indicate your intentions to other road users unless you are changing from lane 2 to lane 1 in front of the vehicle you just had overtaken and you are really, really sure, that you don’t have to.”.
Simply rule: Want to change lane? M-S-M.