Danger: Deep Water, said the sign behind Nick Clegg as he visited a hedgehog conservation area yesterday. The Liberal Democrat leader was starting his election campaign in unpromising surroundings. As he steers his ship towards disaster he can at least show elegant irony.

The Lib Dems could once wield the power of kingmakers in a hung parliament. Now that role has been usurped by the Scottish Nationalists. The party is overtaken in the polls by Ukip, and in some places by the Greens. It has never been easy to define the concept of "liberal democracy" in Britain. Now it is unnecessary. There is competition even for the "dustbin" vote, and from parties with targeted causes.

Clegg's performance in the 2010 election debate was so dazzling that he was lauded as second in popularity only to Churchill. I wrote unkindly that this was as good as it was going to get. Clegg would not be king but kingmaker. And the king, once made, would hold him trapped in craven subservience.

Cameron stuffed his government with senior Lib Dems, thus ensuring what proved their lasting loyalty.

Few gave the coalition its full five years. There were too many angry Tories and rebellious Lib Dems, plus the near certainty of a resulting Lib Dem collapse at the ballot box. Yet Clegg handled his inevitable humiliation with skill and even some panache. The party's previous attempt at such an alliance, by David Steel with the Callaghan government in 1977, was a shambles.

Clegg clearly set out what he would require of the coalition. He claims that taxes were lower, welfare higher and austerity less severe, thanks to him. In return he held his MPs to the coalition, as was required of him, through thick and thin, through recession and into recovery.

His one lingering hope now is that Cameron might scrape enough MPs to be within reach of a majority over the new Labour/SNP bloc. Clegg thus mused yesterday that he would not rule out agreeing to an EU referendum. He burned his fingers with reckless election promises on tuition fees in 2010.

Such a coalition is near inconceivable. If the Lib Dems went back into bed with the Tories they would face the sort of elimination they saw after the 1930s, when its MPs were forced to plead with the Tories not to stand against them.

Clegg's other hope, that Labour might need him to back up the SNP, is mere gasping for breath. But as the good ship Lib Dem dips beneath the water, we can salute the captain on the bridge for a noble last voyage. As the bard would say, he has done the state some service.

• This article was amended on 1 April 2015 to clarify the status of the Parkridge Centre, a nature reserve, which was referred to as a hedgehog farm.