The Broadcasting Standards Authority is investigating Breakfast host Paul Henry over comments he made about singer Susan Boyle.

The authority has received five complaints following TVNZ's finding against Mr Henry, last month.

The Breakfast presenter referred to Ms Boyle as "retarded" in November last year, sparking complaints.

"Here's the really interesting revelation: she is in fact retarded ... and if you look at her carefully, you can make it out," Mr Henry said on his Breakfast show.

Ms Boyle was born with minor brain damage and has learning difficulties.

TVNZ upheld the complaints on the grounds of "good taste and decency" and Mr Henry issued a written apology.

But at least eight complainants were not satisfied with the apology and have appealed to the BSA. More could come forward with the BSA's 20 working day deadline being extended to early February to take into account the holiday period.

BSA head Dominic Sheehan said some of the complainants have also appealed on the grounds that Mr Henry's comments were discriminatory.

"We'll be looking to see if [the apology] was sufficient in this case and if it wasn't, of course we might order something within our powers to occur. The discrimination complaint is a brand new thing and we'll be looking to see if [TVNZ] should have upheld that," Mr Sheehan said.

He said the BSA can fine TVNZ up to $5000 or take advertising off the broadcaster if they find in favour of the complainants.

TVNZ spokeswoman Megan Richards said the complaints to the BSA were "all part of the process".

"That's very usual. There is almost always one person and it is immaterial how many, actually. All it takes is one person to have the matter considered under the BSA process so we're quite prepared for it and expect it will take some months for any outcome," Ms Richards said.

She said TVNZ stood by their finding that the comments were not derogatory or discriminatory.

One of the original TVNZ complainants was IHC New Zealand chief executive Ralph Jones.

Last month Mr Jones said he was pleased with Mr Henry's apology.

"Paul's apology will make things easier for people with intellectual disabilities, who have been enormously embarrassed and offended by what he said," Mr Jones said.

At the time, TVNZ spokeswoman Megan Richards said there would be no punishment for Mr Henry.

"We see this process about establishing boundaries, not about punishing or banning words," Ms Richards said.

In his apology, Mr Henry said he never intended to cause offence.

"It upsets me greatly that anyone would imagine I had intended to cause offence or hurt over this or any issue. I am sorry that some people have taken what I said in a way that I never intended," he said in a statement.

The TVNZ complaints committee found that although Mr Henry meant his comments to be "humorous", they found that the language and manner of Mr Henry would have offended a "significant number of viewers".

Mr Henry has previously been taken to the Broadcasting Standards Authority when he made comments about a Greenpeace spokeswoman having facial hair.

The complaint was not upheld by the BSA who found that TVNZ had already taken sufficient action.