It is legal to use a limited amount of another’s work without their permission for caricature, parody or pastiche.
The words have their normal meanings.
Fair dealing allows you to use a limited amount of someone else’s work. If longer extracts are required you will need to get permission from the copyright holder.You cannot expect to be able to use an entire musical track or video and fall within this exception.
By definition a parody does involve humour or mockery but it does not have to be aimed at the original creator. You can use it to make a point on any topic. The humour element has yet to be tested in law.
You may wish to read this article from the Daily Telegraph.
These changes to copyright law do not alter the laws on defamation (libel or slander). You may be sued if your work is seen as defamatory.
There are further protections under the copyright laws for the original creator of the work and if your use of their material amounts to “derogatory treatment” the rights-holder will be able to take legal action.