UK politics: meaning of 'withdrawing the whip'?

I’m a Brit myself, and I understand most of the jargon involved in our quaint political system, but this phrase has me baffled.

When a politician has done something of which his/her own party disapproves, it is sometimes said that he/she ‘had the Whip withdrawn’.

What does this mean? What, if anything, actually happens in practical terms? And since the party Whips are the heavies who make sure MPs toe the line, why would having this ‘withdrawn’ be a punishment? If an MP is of a maverick or independent turn of mind, surely she/he would actually quite enjoy not being hassled by the party Whips?

Correct me if I’m wrong, but I believe “withdrawing the whip” means kicking the offending MP out of the party, which means, of course, that the MP won’t get party support for his or her bills, or get the help of the party organization during the election.

When the whip is withdrawn from an MP, it means that they are expelled (usually temporarily) from the parlimentary party of which ever party they represent(though AFAIK they will still be a member of the party itself), so they are no longer an MP for that party and are effectively an independent.

(Note: partly for foreign readers)
The Whips (from the ‘whippers in ‘ who marshall a pack of foxhounds) are responsible for getting the Parliamentary vote to turn up at the right times, telling them which way the party wants them to vote on a measure, and the day-to-day discipline of the Parliamentary party. All the major parties in the House have them. Each week they send out to their M.P.s a piece of paper called the whip (these days probably an email) with the timings of the various votes expected to come up in the coming week. The importance of the various votes is denoted by the number of times the relevant passage is underlined. A one-line whip denotes routine business which can be ignored if the M.P. has business elsewhere. A two-line whip denotes important business from which absence will not normally be excused unless the M.P. has a ‘pair’ i.e. an arrangement with a member of the opposing party that neither of them will attend the vote and their combined absences will cancel out. (Pairing arrangements are particularly valuable when the Government has a large majority and many majority party M.P.s will be unable to find a pair and will have to keep hanging around the House for hours in case they are needed for a snap vote.) A three-line whip denotes exceptionally important business for which absence will not normally be excused except for serious illness (and sometimes not even then. In the late ‘70s, when the Government’s majority was small they were bringing dying M.P.s to the House in ambulances and carrying them through the lobbies on stretchers to vote). Defying a three-line whip is tantamount to secession from the party, temporarily at any rate.
The whips are also the leadership’s eyes and ears in the Parliamentary party, warning it of dissension and trouble ahead. They also maintain a Little Black Book full of dirt that they can use to blackmail members into toeing the line (X is a drunk, Y is a closet gay, Z has had shady financial dealings etc.)
Having the whip withdrawn cuts you off from the party’s support machine, labels you as a bad boy, and can lead to being deselected as the party’s candidate for the next election in your constituency, although if the government’s hand is weak (as with Ian Duncan Smith and the other Maastricht Treaty rebels) it cannot hurt you too much without hurting itself