What is the procedure for hiring a professor? When a department head needs a faculty member, how is the process of hiring one started and conducted (at least in US and UK universities)?

Of particular interest is the following;


Finance: Department head should ask the Dean for financing the salary? Who is the final decision maker?
Selection: Is the department head responsible for forming the search committee? and is he responsible for approving the qualifications? Can higher officials (e.g. Dean) interfere in the selection?
After the selection, how are the official matters handled? Who signs the contract? and who can terminate it (if not tenured)?
What is the role of human resources in this process?
EDIT: Added dates to give a sense of the timeline.

Here's how the process works at my university (US). 


The department votes (March or April 2014) to request a new hire or not. Usually at this point they will also specify--is this a hire in some particular field, or do we just want to try to get the best person in the field, regardless of speciality. This request is passed to the provost and dean.
If the request is approved (May or June), the department forms a search committee which writes and circulates the job ad (Sept or Oct).
Once all the applications for the job are in (Nov), the search committee reads the applications and selects between 15-25 people to interview at our big disciplinary meeting (January 2015). This is a first round interview that will usually discuss scholarship and maybe a little bit about teaching. 
Of that field of 15-25, the committee will select three finalists to bring to a second, on campus interview. (February) The on campus interview is much more strenuous, usually lasting a day or two. At our institution it always includes a public job talk, which presents some facet of the candidates current research before the full faculty and graduate students. Some places it also includes a teaching demo. Invariably there is also a dinner after the talk at which the candidate still needs to be pleasant, conversational, and collegial. 
After all the on-campus interviews have been conducted, the department meets and discusses who they want to pick. (Late Feb, Early March) Usually this involves a vote. At some places the faculty's vote is binding, at some places the faculty vote is simply advisory and the committee makes the official recommendation. But, at every school I've heard of it is the Dean or Provost who actually makes the final decision. 
So, let's say the department has recommended candidate X to the Dean and the dean has no objection. Now the dean will call candidate X and offer him or her the job.
Usually some rounds of negotiation will follow. If the candidate has other offers, then usually the dean will have to improve the offer. Once a verbal agreement is made, the dean sends a contract to the candidate to sign and return. 
Once the dean signs the returned contract, then, presto the candidate is officially a tenure track faculty member. (April or May 2015)