If there are only two major parties it is almost inevitable that one of them will get more seats than the other one and all the other minor parties combined and form a majority government.

If there are three or more major parties it is almost inevitable that none of them will get an overall majority.

With many people who might previously have seen a Lib Dem vote as a wasted vote now seeing them as worth voting for at last, and assuming Labour don't drift away to become a minor party, it looks like we could see a roughly equal three way split in any future election.

Does that mean we will always have coalition government, along with the bizarre situation of the party who comes third being the only one which is virtually guaranteed to be part of that coalition as they choose which of the other two to join ?

Not necessarily. The Scottish Government in Holyrood has so far seen two coalitions and one minority government. You might also get a lot of LibDems, unhappy that they've sided with Cameron, defecting to Labour next time, thereby having a Labour majority (of seats).

If they introduce PR, then coalitions look a lot more likely.

If PR happens then yes we'll have coalitions from now on

Only if PR is implemented which at present looks unlikely.

If the current coalition hangs together and does a decent job, the Tories stand a good chance of getting a majority at the next election

If they do a bad job (or at least are perceived to have), Labour stand a good chance of getting a majority at the next election.

Lets hope so.

Both the big partys are really coalitions anyway. Labour with the Marxist at one side a to the Christian democrats at the other. Tories with the one nation lot to the swivel eyed xenophobes.

Given PR and a generation we might well see a real realignment with both labour and Toy effectively splitting

With many people who might previously have seen a Lib Dem vote as a wasted vote now seeing them as worth voting for at last

That might be true, though lots might not be too happy about the compromises they have had to make.

You might also get a lot of LibDems, unhappy that they've sided with Cameron, defecting to Labour next time, thereby having a Labour majority (of seats).

That's sort of my point.
If the Lib Dems become a major party in their own right, their supporters won't have to decide which of the other two parties they want to vote for to keep the other one of the big two out. They can finally vote for the one they want in.
Unless one of those other two then loses most of its support, we will then have three big parties.

That might be true, though lots might not be too happy about the compromises they have had to make

.
But if they become an equal third party, they won't have to make such compromises.

There must be a lot of people who support either the BNP or the Greens, but won't vote for them as they see it as a wasted vote and it doesn't look like that will change any time soon.
The Lib Dems appear to be reaching that critical mass where they are no longer seen as a wasted vote.
It just looks to me like we have now got three major parties and we may never see a majority government again.

The Lib Dems appear to be reaching that critical mass where they are no longer seen as a wasted vote.

Did you not notice that the LibDems actually lost seats at this election? The only reason they have any power is that the first place party did worse than normal and the second place party better.

If the current coalition hangs together and does a decent job, the Liberals stand a good chance of getting a majority at the next election.

😀

Ask yourself this: How does a party with absolutely zero chance of election (under our present voting system), manage to reliably secure one quarter of the vote?

A possibly answer: they are much more popular than the vote indicates

So Alternative Voting may benefit the LD's a lot. Consider that few seats are won with overall majorities. As a middle party, LD's might be everyone's second choice. So the instant run-off could give them the majority in most seats, making them the largest party.