I am very surprised that professional drivers are having this conversation.
Please tell me when in your training you were told to flash your lights to let overtaking vehicles know they are clear. The flashing of headlights on a road means I am here you may not be already aware… 
Highway code -
110
Flashing headlights. Only flash your headlights to let other road users know that you are there. Do not flash your headlights to convey any other message or intimidate other road users.
111
Never assume that flashing headlights is a signal inviting you to proceed. Use your own judgement and proceed carefully.
The older highway code used to mention that truck drivers had thier own reasons for flashing but that has now been scrapped and I think I know one of the reasons why -
- the mirrors on trucks used to be silly little things like some of the double decker bus mirrors are now but they have been replaced by the ones we now use which give a much better view.
To see when the trailer was clear in the old days was a bit of a nightmare when trying to judge it in a compact sized mirror 
Smee:
I am very surprised that professional drivers are having this conversation.
Please tell me when in your training you were told to flash your lights to let overtaking vehicles know they are clear. The flashing of headlights on a road means I am here you may not be already aware…
Can relate to that. On one of my first trips over the water i was indicating my intention to overtake a truck on an autoroute in Italy, sees a car coming up in the offside lane, he flashes his lights , i pull out and after overtaking i pull back in .Car driver blasts horn and gives me Gareth Hunt “coffee beans” gesture . . . .lesson learnt 
I havea length of string the same lenght of my unit that I chuck out of the window to the driver I am passing, when it goes slack it means that it has pulled out of his fingers and I can safely pull in. Jeez you guy’s complicate things with your flashing headlights. 
Never react to a flash I know how long I am, but always acknowledge a flash as its the right thing to do. If overtaking a line and someone wants to pull out I will let them 1 mile an hour and 400yds lost isn’t going to bother me. Being seen as an arse is!! 
ROG:
Highway code -110
Flashing headlights. Only flash your headlights to let other road users know that you are there. Do not flash your headlights to convey any other message or intimidate other road users.111
Never assume that flashing headlights is a signal inviting you to proceed. Use your own judgement and proceed carefully.The older highway code used to mention that truck drivers had thier own reasons for flashing but that has now been scrapped and I think I know one of the reasons why -
- the mirrors on trucks used to be silly little things like some of the double decker bus mirrors are now but they have been replaced by the ones we now use which give a much better view.
To see when the trailer was clear in the old days was a bit of a nightmare when trying to judge it in a compact sized mirror
totally agree Rog
tachograph:
manowar:
I agree though that some drivers do pull in a bit too quickly before you’re able to flash them! Not too much of a problem so long as they keep a good momentum.
Sorry but if I’m forced to brake to keep a reasonably safe distance between us I consider it to be a problem, not one I’ll lose sleep over but still unacceptable and unnecessary.[/quote
I like to be able to see tarmac in front of me - I hate those who stick the indicator on and just move on over without being invited, and only inches from my nose! It also irks me a tad when someone flashes me in and I can tell i’m not anywhere near far enough past him - but then they get really persistant - do these people not like being able to see anything out of their window but my broad rear?!
I have a tip that not many have heard of - or use -
Judge the distance on a motorway (or any other road) by the lane lines (short or long ones).
One lane line = 10mph so when a truck passes at about the same sort of speed leave about 5 lanes lines gap before flashing and it will pull in at 6 - easy.
As the overtaking driver it is also easy to see the lane lines increasing behind from the rear of the overtaking truck to the front of the truck being overtaken and to judge the pull in by them.
I DON’T CARE! Mind you i do like giving arc eye by flashing in when its dark
ROG:
Highway code -110
Flashing headlights. Only flash your headlights to let other road users know that you are there. Do not flash your headlights to convey any other message or intimidate other road users.111
Never assume that flashing headlights is a signal inviting you to proceed. Use your own judgement and proceed carefully.The older highway code used to mention that truck drivers had thier own reasons for flashing but that has now been scrapped and I think I know one of the reasons why -
- the mirrors on trucks used to be silly little things like some of the double decker bus mirrors are now but they have been replaced by the ones we now use which give a much better view.
To see when the trailer was clear in the old days was a bit of a nightmare when trying to judge it in a compact sized mirror
But what if said mirrors are obscured by tassled curtains /pelmets 
And what ever happened to the quick sidelights on/off gesture ?
Whilst this subject has been raised, can somebody explain why when I flash a truck in on the motorway in my bus only a few flick the indicators on to say thanks, the vast majority dont, only for them to overtake another truck get flashed in and flash the indicators in response?
yes,but on the other side of the coin,ive lost count at the number of times ive flashed in a national express,usually with windows full of terrified faces zooming past my drivers mirror,only for afore mentioned coach to pull in and not thank me for my trouble.
“Suedehead” You "look in the mirror and guess when to come back in"Â 
. . . . are you for real ?
Maybe , " guess " was the incorrect termonology , i apologise…but after 20 years of class 1 i reckon i know where the end of my trailer is   Â
DAF95XF:
Whilst this subject has been raised, can somebody explain why when I flash a truck in on the motorway in my bus only a few flick the indicators on to say thanks, the vast majority dont, only for them to overtake another truck get flashed in and flash the indicators in response?
Silly question,why are you driving a bus down the motorway?
el sumo:
“Suedehead” You "look in the mirror and guess when to come back in"ÂMaybe , " guess " was the incorrect termonology , i apologise…but after 20 years of class 1 i reckon i know where the end of my trailer is
Fair play, not nice when somebody might "guess"when its safe to pull back in
Suedehead:
DAF95XF:
Whilst this subject has been raised, can somebody explain why when I flash a truck in on the motorway in my bus only a few flick the indicators on to say thanks, the vast majority dont, only for them to overtake another truck get flashed in and flash the indicators in response?Silly question,why are you driving a bus down the motorway?
COS HE’S A BUS DRIVER MAYBE?
Suedehead:
Silly question,why are you driving a bus down the motorway?
To get to somewhere to start a service, its quite often easier to get to somewhere like Farnborough or Andover via the M3…
MR VAIN:
Suedehead:
DAF95XF:
Whilst this subject has been raised, can somebody explain why when I flash a truck in on the motorway in my bus only a few flick the indicators on to say thanks, the vast majority dont, only for them to overtake another truck get flashed in and flash the indicators in response?Silly question,why are you driving a bus down the motorway?
COS HE’S A BUS DRIVER MAYBE?
Very clever but its not very often ive seen a bus on a motorway 
Splittin hairs! Coach driver then.
gettin daft on ere! or is it just me??silly questions…dafter people?
That old chestnut again