(edited version from full text on Liberal Polemic)

I would not be so sure that diversifying beyond single-issue status is beyond UKIP. There is now a lot of space beyond Cameron Conservativism, and plenty of disaffected Thatcherites looking for a home.

Most of the Tories I know make wistful noises about UKIP, wishing it could be more serious and more broad in its appeal. They also generally think Farage its a Muppet (I wonder why!).

However, crucially, UKIP is small. A boost in membership from Tory defectors and they could tilt the balance of power and transform it into a serious (albeit small) party.

The question, therefore, is not whether Farage can move UKIP from being a single-issue to a multi-issue party: he can, but he'd probably be a casualty of the change, as a more serious contender took over.

The real question is, does UKIP actually benefit from being a single issue party? UKIP has thrived (nine MEPs!) by picking up anti-European votes in a political field with no genuinely anti-European party that does not have other issues which might alienate voters (fascism and communism being obvious examples). If UKIP does become a proper political party, they might find that many of their voters are put off by the specific policies they advocate.

Normalisation may not in fact be UKIP’s road to success but an act of suicide manifesting itself as extreme hubris.

Cameron clearly alienates many hard-core Tories, but
crucially not on the touchstone of Europe. 
He carefully matched the pledges made by Liam Fox during the Conservative
leadership election.  Though he's had trouble delivering them, it will be
other issues that make people leave first.

If they did this on a large scale would they seek our Farage or a separate
outfit of their own? 

The left has countless different socialist groupings which
just don't exist on the right.

The right might see themselves as more disciplined, but their
pent up frustration is growing (see today’s ‘Rightwing MP urges Tories to be
bold on tax’ in the FT)

I suspect we would see a little balkanisation on the right with
UKIP joined by a few others for at least a little while.