Wendy Alexander’s leadership has been swept away in a squall of dirty tricks and political expediency. There was certainly no natural justice in pronouncing a sentence, however lenient, with such cynical timing that she would be forced to wait months before she could serve it and move on.

Yes, she was wrong not to make a full and prompt disclosure of her donations. I have never understood why ambitious and otherwise skilful politicians do not tell their staff always to err on the side of over-disclosure rather than the opposite. But it certainly was not an offence that merited bringing her career in the Scottish parliament to an end.

It may well be that the SNP was hoping to wound her rather than kill her off. It has suited its purposes admirably to have a Labour leader unable to raise her head above the parapet long enough to land any decent blows on the nationalist administration.

The SNP politicians would probably have gone off on their summer holidays quite happy to see her crippled politically but limping on. By resigning, she has denied them that. But Alex Salmond will not waste time mourning her passing. He is nothing if not a formidable tactician.

The timing of the standards committee findings left him sitting pretty in a win-win situation. Having no leader in the crucial weeks ahead is hardly better for Labour than having a damaged one. And having no heavyweight leader in reserve, waiting to take over, is the worst of all worlds. Some in Labour’s ranks may welcome the chance for a fresh start under a new leadership, but that is a dangerously short-term view.

Gordon Brown, who is a match for Salmond as a political tactician, will not be seeing it that way this weekend. Alexander’s resignation is a serious setback and he knows it.

It certainly will not make holding Glasgow East any easier in the forthcoming by-election. And Brown needs Labour to start winning a few battles rather than losing every single one. Holding David Marshall’s seat, with its 13,500 majority, will not turn around the prime minister’s fortunes, but losing it would be another grievous blow.

It is not Glasgow East that will be troubling the prime minister most, however. He will be looking farther ahead than that, to Scotland’s future within the union, something that strikes to the core of his fundamental beliefs. There is a growing risk that when his time does come it will be said that, albeit unwittingly, he endangered the union that he fought so hard to preserve.

Labour has always made the case that Scotland is stronger, wealthier and more influential inside the union than outside it and that is not going to change whoever succeeds Alexander. But her replacement is all but certain to put a greater distance between Scottish Labour and the leadership in London.

Alexander saw the need for a bit of that herself, but when she told the nationalists to “bring it on” and call the referendum, she was forced to back-pedal by, among others, Brown himself.

He is likely to have less influence on her successor. Alexander is a child of pre-devolution politics. She is of the Donald Dewar-Brown school, having polished her skills by watching them and learning. She was plugged into their thinking and while she had her own very clear ideas about the modernisation of Scottish politics, she was their creation. So when the prime minister said he wanted something done his way, she found it hard to say no. When “bring it on” fell by the wayside, the message seemed clear. Real power still lay outside Scotland.

The next leader will have cut his or her teeth in a very different environment. Telling the party at Westminster to mind its own business is likely to come much more easily to them. They will be tempted to do so not just because Brown’s government is damaged goods, but out of a belief that they will be strengthening the case for devolution, showing that London does not always call the shots.

Labour grasped the true meaning of devolution, its own creation, too late in the day. How much better it would have been if some of Scotland’s really big hitters had opted for Holyrood rather than pursuing their Westminster careers. The presence of Jim Murphy or Douglas Alexander would have shown that in Labour’s own eyes the Scottish parliament really was a power in the land. A new, talented generation of leaders would have been nurtured and might now be ready to take devolution forward. Instead, we are likely to get a Labour leader who would be lucky to earn junior ministerial rank at Westminster.

This is the nightmare scenario. A new leader sees association with Brown as a liability. When there is a crisis in Scotland, the phone in Downing Street does not ring. Labour argues for more devolved powers, perhaps repeating the call for an early referendum, but appears embarrassed by its own UK government and prime minister. All well and good if Salmond is about to have a brainstorm and agree to a referendum in the next year. But that is not going to happen.

Slowly but surely, the squall that has capsized Alexander builds up to the perfect storm. Labour fails to recover either in Scotland or the UK. Suddenly, Brown is no longer in Downing Street and Britain is led by not just by a Tory but an Old Etonian to boot. Now, ever the canny tactician, Salmond calls his referendum. “Who governs Scotland?” he asks.

Whoever Labour picks to replace Alexander had better have a very good answer to that one. If not, the phone lines between Edinburgh and Downing Street had better stay open so that, between them, they can find one.

Lance Price was deputy press secretary at 10 Downing Street under Tony Blair