Theresa May’s deal with the DUP will fall far short of a full-blown coalition, and is only a step away from minority government • General election 2017 - live updates

The “confidence and supply” deal that Theresa May is trying to strike with the Democratic Unionist party is one of the most hand to mouth arrangements a minority government can use to keep it in power.

This is not going to be a repeat of the David Cameron/Nick Clegg 2010 “rose garden” coalition. A “confidence and supply” arrangement falls far short of a full-blown coalition. It does not involve an agreed five-year programme of policies and may not even involve the junior party holding ministerial office, let alone taking on the role of deputy prime minister.

The 2010 Conservative-Lib Dem coalition was seen in the Tory party as far preferable to a “confidence and supply pact” with the Ulster unionists, including the DUP. As Ken Clarke “joked” during the 2010 election campaign: “In the end, you can always do a deal with an Ulsterman, but that’s not the way to run a modern, sophisticated, society.”

This time, Theresa May is faced with no other option but to try for a limited pact under which the 10 socially conservative DUP MPs agree to support her government in votes that are critical to its survival in office in return for some of their policies being enacted.

But it is one step away from pure minority government, such as Harold Wilson’s February 1974 Labour government, under which the largest party does no deals with any other party but instead relies on the threat of a fresh general election to keep it in office.

What does ‘confidence and supply’ mean?

The Institute of Government says confidence deals “typically make clear that the support party or parties must back the government on explicit confidence votes, and votes on budgets and supply (government spending). In return, the support parties are given government support for specific policy priorities.”

The most recent example in Westminster politics was the Lib-Lab pact of 1977-78 between Jim Callaghan and David Steel. It lasted only 18 months.

DUP will extract a high price to prop up a Tory minority Read more

In the 1990s, John Major found that his battles over Europe and Maastricht in the Tory party, byelections and floor-crossings were whittling away his original majority of 21. In the process he became reliant on the votes of Ulster Unionists to keep the show on the road but Major refused to do any kind of formal deal. At one point, £10m was made available to subsidise heavy electricity users in Northern Ireland and a promise was made that an electricity interconnector cable would be laid across to Scotland.

Such an arrangement is being used to keep the National party in in government in New Zealand in a confidence deal with the Maori party.

It has also been used in the devolved administrations in Britain. In 2007, the SNP did a deal with the Scottish Greens giving them the chair of a Scottish parliament committee in return for supporting the election of Alex Salmond as first minister.

How does it work on a daily basis?

The advantage for the governing party of confidence and supply arrangements is that they know they are not in danger of defeat at every key vote and do not have to give up ministerial posts or negotiate their policy programme with another party. For the smaller party it means they can secure concessions on specific policies without having to sign up to the entire government programme or lose their independent voice in parliament.

The disadvantage is that in areas not covered by the agreement, ie beyond the Queen’s speech on 19 June and subsequent budget, the government still needs to build an issue-by-issue coalition to get business through parliament. This also opens the door for Jeremy Corbyn’s Labour MPs and the SNP to play a far more decisive role over government legislation.

The disadvantage for the junior partner is that they have to back politically unpopular budget plans and have less influence on overall policy.

In order to get its business done the government also needs to get its legislation through the House of Lords, where the DUP only has four peers out of 800.

What difference does the Fixed-term Parliaments Act make?

The Hansard Society says it breaks the link between issues of confidence and the dissolution of a parliament. The act takes away the prime minister’s power to call a general election. Before 2011, if a government was defeated on its Queen’s speech or on its budget, it would be regarded as loss of confidence that would lead to the PM’s resignation and a general election being called. Now the opposition parties are to be given 14 days to form a government and if their alternative coalition can win a confidence vote in the Commons then they will take over without an election.