problem in grammer
the following sentences are from BBC
The PM denied making the abusive outbursts the book accused him of, but was then confronted with claims from an anti-bullying charity that staff from No 10 had called their helpline.

the question is :who can tell me in details the use of "that -clause"?
"that staff from No 10 had called their helpline"
i understand the meaning of this sentences ,but i can not understand them in grammer
i just want a explanation in grammer.I know the meaning ,fdmaxey,but thanks all the same.i just want to know it in the aspect of grammeri know it .thanks Jura,thank you for your explanations and advice.i misundertood these sentences ,and now i know it is not an attribute clause ,it is appositive-clause ,isn't it!

Question

problem in grammer
the following sentences are from BBC
The PM denied making the abusive outbursts the book accused him of, but was then confronted with claims from an anti-bullying charity that staff from No 10 had called their helpline. 

the question is :who can tell me in details the use of "that -clause"?
"that staff from No 10 had called their helpline"
i understand the meaning of this sentences ,but  i can not understand them in grammer
i just want  a explanation in grammer.I know the meaning ,fdmaxey,but thanks all the same.i just want to know it in the aspect of grammeri know  it .thanks  Jura,thank you for your explanations and advice.i misundertood these sentences ,and now i know it is not an attribute clause ,it is appositive-clause ,isn't it!

Answer

Hi Bruce, I am guessing that you want an explanation of the use of 'that' as a relative pronoun in English grammar[ not grammer]
Using That, Which, and Who as Relative Pronouns

That, which, and who when used as relative pronouns each has a distinct function.

In modern speech, which refers only to things. Who (or its forms whom and whose) refers only to people. That normally refers to things but it may refer to a class or type of person.

Examples: That is a book which I need for the class.

These are the books that I need for the class.

He is the man who will be teaching the class.

They are the type of people who would lie to their mothers.

They are the type of people that would lie to their mothers.
    (That is OK here because it is a class or type.)

Some teachers also tell you that that should be used with restrictive modifiers and that which should be used with nonrestrictive modifiers. Historically, there is little evidence that this "rule" ever had a significant effect on English expression, but writers should be aware that some correspondents have been taught this practice.

Sometimes using which for a restrictive modifier can make a sentence sound better, especially if the sentence already uses the word that (as in the first example above).

This "rule" can cause confusion with multiple clauses, questions, or certain constructions and compounds which use that. It is better to communicate more clearly than to worry about a questionable "rule."

Answer

An anti-bullying charity organization made a claim that people from No. 10 [No 10 Downing Street is the address of the British Prime Minister and his staff] had called their [the charity's] telephone helpline.
The purpose of an anti-bullying organization is to help those that have unfair pressure put on them by co-workers or bosses.  If the staff of the Prime Minister is complaining about being bullied - as claimed by the anti-bullying organization - this would be a serious embarassment for the Prime Minister.  His staff is seeking protection from either him or those that work for him.