Early August, with the London Olympics in full swing, might seem a strange time for the Prime Minister to communicate a major policy shift. But much depends, of course, on how many waves he wants it to make and the answer might well be: as few as possible. For if, as is confidently expected, David Cameron announces that the Government is to abandon House of Lords reform, there is bound to be political fallout and there will be those who will seize upon it to forecast the destabilisation, if not the imminent end, of the Coalition.

The significance of such a decision should certainly not be underestimated. Reform of the House of Lords was a pillar of the Coalition Agreement. It had been a central demand of the Liberal Democrats and was right up there with a referendum on electoral reform as a pre-condition for the party to enter government at all. With the cause of electoral reform lost – after last year's swingeing No vote in the referendum – the fate of Lords reform gained additional importance as evidence (or otherwise) of the influence within the Coalition of the Liberal Democrats collectively and that of their leader, Nick Clegg, personally.

The Liberal Democrats will thus be the chief losers if House of Lords reform is abandoned. Mr Clegg, in particular, is likely to face renewed questions about whether his party exerts any real power in the Coalition and whether it might not have lost more in electoral credibility than it has gained in terms of a share in government. Not for the first time Mr Clegg can expect a difficult party conference in the autumn.

The coming conference season, however, may also explain why Mr Cameron has apparently chosen to shelve Lords reform sooner rather than later. While there was support in the House of Commons for the Lords Reform Bill in principle, there was, crucially, a sufficient number of Conservative dissenters to block approval of a timetable. Mr Cameron delayed the vote in the hope of persuading enough of his MPs to enter the lobby behind him. An early announcement that the project is to be abandoned will be tantamount to an admission that he has failed. It appears that he has decided to cut his losses, at a time when the country is otherwise engaged, rather than exacerbate tensions within his party by fighting on into the next parliamentary term.

Nor, regrettably, is Lords reform likely to be the only progressive constitutional measure to be halted. When it first emerged that Lords reform was running into trouble, the Liberal Democrats threatened that, if the Conservatives blocked it, they would block proposed constituency boundary changes in return. It will be hard for the Liberal Democrats not to carry out that threat now, without looking weaker than they already do. In fact, such a move could work to their advantage, because they – and Labour – were set to lose seats, while the Conservatives stood to gain. The Liberal Democrats could even enjoy the last laugh, if – as is possible – sticking with the old constituency boundaries costs the Conservatives an overall majority at the next election.

Warnings of permanent damage, or even a premature end, to the Coalition, however, are probably overblown. If Mr Cameron, who is a supporter of Lords reform, has had to bow to prevailing opinion in his party, this will be proof not of his strength as party leader, but of his weakness. Neither he nor Mr Clegg can afford to leave the Coalition; they need each other, and each other's parties, if they want to stay in power.

This is not to say that nothing has been lost. Within only a little more than a year, three major constitutional reforms – of the electoral system, the House of Lords and constituency boundaries – will have foundered. The Coalition may soldier on, but it has grievously missed a possibly unique opportunity to make Britain's political system fitter for the modern age.