11/05/2015 06:03 BST | Updated 10/05/2016 06:59 BST

Five Years of Keeping Promises?

David Cameron has spent the past five years building a rod for his own back. "Promises, promises" the electorate will now be saying to themselves − both the people who did and the people who did not vote for the Conservatives.

He has promised not to raise VAT and income tax, not to cut child benefit, not to reduce spending on the NHS, and at the same time to significantly reduce the deficit. These undertakings stole a march on the Labour Party in the Election 2015 campaign.

He has promised devolution max to all nations of the UK. An assurance which helped to empower the SNP and neuter the Labour Party and the Liberal Democrats in Scotland.

He has promised an in/out referendum on membership of the European Union and renewed his commitment to reducing net migration to below 100,000 per annum. These pledges drew much of the sting from the Ukip challenge.

But amongst the astonishing things about the Election 2015 victory is that Cameron has a track record of making and breaking such electoral promises. In 2007 Cameron offered a "cast-iron" guarantee of a referendum on the Lisbon Treaty. In the run up to the 2010 General Election he made a "no ifs, no buts" promise to reduce net migration to the tens of thousand and even told voters "If we don't deliver... vote us out in five years' time".

Five years have been and gone and still no referendum and net migration has risen. Yet UK voters have not kicked out the Tories.

An entirely different fate has befallen the Liberal Democrats of course. The failure to keep a clear manifesto pledge on higher education tuition fees is a crime for which the British people could not pardon Nick Clegg.

How then do politicians avoid breaking promises and frustrating the legitimate expectations of the electorate? One strategy is to make unfalsifiable promises, with plenty of get-out clauses and caveats. Think of Ed Miliband's doomed tablet of stone and its vague and platitudinous pledges ("A strong economic foundation").

Another strategy, of course, is simply not to be around when the reckoning happens. By declaring now that he intends not to stand in the 2020 General Election Cameron has made it impossible for the electorate to hold him personally responsible for breaking yet more promises.

Perhaps politicians in the future might consider a third strategy: to make only a small number of specific, clear-cut and decisive commitments which they have overwhelming evidence-based reasons to believe they can and will deliver. Then perhaps the pledges they make will seem to people more like credible commitments than empty promises.