The wider significance of the Liberal Democrat victory in the Gurkha debate yesterday is twofold.

Well, threefold. To get the bleeding obvious out of the way first, it’s another strangled warble in the painfully operatic death of Gordon Brown’s political career (y’know, the ones that never … quite … diiiiiiii-iiiiiiii-iiieeeeee!)

Secondly, it may come to be seen as a defining moment in Clegg’s leadership. No media source that I am aware of is denying him full credit for having taken up the Gurkhas’ cause as soon as he reached office. An otherwise generous David Cameron felt the need to interrupt Clegg yesterday during their joint press conference with La Lumley, halfway through Clegg’s perfectly articulate answer to a question which was put directly to him. That interruption is a telling sign of who was political top dog yesterday afternoon.

The most successful parliamentary moment in Clegg’s leadership so far may become particularly significant if this afternoon’s debate on MPs expenses – where he has also been leading the way, having been the first leader to moot the idea of a three-way meeting – turns out equally well for the two opposition parties.

A nice parallel in several ways is Paddy Ashdown’s championing of the Hong Kong citizens who applied for British passports in 1997. This was similarly a niche issue at first which slowly rose to top of the national discourse and established Paddy as someone who had Done the Right Thing. The Iraq war, of course, is another parallel – all three fitting enough for a party of internationalists.

But thirdly, and most significantly, the Gurkha debate constituted a sudden and spectacular meeting of minds between liberalism and the self-styled “moral majority”. Andrew Neil commented that he had never had such a flood of emails after PMQs, and all in support of the Gurkhas cause.

This is because, and let’s not shirk this issue, the Gurkhas hit on some rather old-school buttons. The moral majority like Gurkhas, they’re brave and love Britain etc. And the same moral majority has spent some years railing against excessive immigration of the undeserving. Suddenly they have a clear-cut case in front of them of the deserving being denied the right to immigrate. It enables them to affirm their support for all things British – or better still Anglophile – military and citizenly, while also denouncing all the “murderers and terrorists” whom they imagine to be spilling over the borders. As a fable, the story of the Gurkhas is about as neat and Middle England-flavoured as you can get. And Joanna Lumley was involved. No wonder the moral majority went wild for the Gurkhas.

But I’m not being dismissive of the moral majority (no, that was just good-natured joshing), because there was, under all the prejudiced persiflage, a strong moral conviction and it went like this: if them, why not them. If this, why not that. If the willingness to die for a country, why not the right to live in it. The kind of people who write into Andrew Neil might call that morality. We liberals usually call it fairness – Clegg departed from our usual touchy-feely inoffensive script yesterday in using the M-word.

Of course, our “fairness” and their “morality” are not quite the same. Our “if them, why not them” works equally in reverse, against the social tyrannies of the moral majority. Tomorrow we’ll find ourselves fighting an unpopular cause again. Evan Harris had it neatly summed up at a session during the Convention on Modern Liberty, when he challenged a Conservative panel on their happy claims to be liberals – “What about,” he said, “The people you don’t like?” Would this enthusiasm for localism, for social enterprise, and for freedom from government control, extend to all, he wanted to know? Or just to the approved causes, as now? Aren’t we just looking at a set of people with different approved causes in the Conservatives?

This is the question we need to keep asking them, perhaps all the more so after the co-operation on the Gurkhas. As can be clearly seen from their marriage tax proposals, Conservative social engineering is, basically, just Labour social engineering in old-fashioned clothes. I hold no faith whatsoever that they even begin to understand why Nick Clegg has championed the cause of the Gurkhas, for all that they cheered him on yesterday when he used the words “moral” and “decency”.

As Mill observed, sometimes  that which purports to be a fixed moral code amongst the moral majority is in fact a social tyranny, often highly specific to its time. “If them, why not them” is a principle that many who supported the Gurkhas’ cause can pick up and put down as it pleases them. Another time, their core “moral” message may be nothing more substantial than “I don’t think that’s very nice” or “It hasn’t always been done like that”. Dominic Grieve acknowledged this beautifully at the Convention when he said that what held the right back from full authoritarianism was the idea that “one’s grandfather might have disapproved”.

If that seems an oddly mutable thing to come out of the mouth of a decent man in an avowedly “moral” party, it’s because it is. And it comes as a bit of a shock to me, as someone who would sooner gnaw their own leg off rather than tell someone how to live, and gnaw their leg off sooner than have them tell me, that we liberals are actually the guardians of morality. Morality is not a set of social no-nos. Decency is not what the Daily Mail says is ok this week. True moral values are fixed, they are not subject to social or religious fashions, and they deal with all equally – did so even before the Enlightenment. The “if them, why not them” principle, and that other liberal stand-by, “do no harm”, are at the heart of most ancient moralistic religions.

So are other things, of course – but it’s interesting how followers of those religions have apparently been able to tell the difference without any trouble. We must presume that the many millions who call themselves Christians but who do not advocate the stoning to death of adulteresses and homosexuals are guided by something. They have successfully separated the abstract and eternal from the particular and timebound.

That separation is precisely what liberalism is all about, what Evan Harris was getting at during the Convention on Modern Liberty, and what Nick Clegg put across so successfully yesterday.

Maybe we need to follow Clegg’s lead, stop calling this thing we do as liberals “fairness” and call it by its older, proper name.