I referenced it earlier but happy to paste it here again:
BBC 'receives 100,000 complaints' over Prince Philip coverage - BBC News
At the very bottom of the report...
"On Saturday, the BBC put a dedicated form on its website to allow viewers to complain about the TV coverage, in recognition of the volume of complaints.
The form was removed later that day, after the number of complaints began to fall, the corporation said."
If the form was only up for a few hours it probably was the same one I saw, although I can't remember when I clicked on the link.
There was no space for text on that form, although the wording was something like 'if you wish to complain about the coverage, fill in your email and we will send our response when it's available'.
I see the BBC has so far declined to confirm the number of complaints, but The Sun almost certainly got their information from a BBC staffer who had a good idea.
The fact the BBC followed The Sun story and didn't deny it is confirmation of a sort.
Ever easier access to the internet will push complaint numbers higher.
For example, I wonder how many of the 40,000 who complained about Brand/Sachs would have done so if they had to write and post a letter.
My guess is nowhere near the number who did so.