It has been widely reported today that the Conservative party have come to a £1Bn+ deal with the Democratic Unionist Party (DUP) to prop up their minority government, which got me wondering what are the key differences between a 'confidence and supply' deal moreover a formal coalition?
This is the UK, so of course there is no formal rule, but based on the 2010 coalition government between the Conservatives and Liberal Democrats, we would expect a full formal coalition to produce a cabinet containing members of both parties, all acting under the convention of collective responsibility. That is to say, with ministers of both parties publicly supporting and defending the government position, regardless of from which side of the aisle it originally came. This didn't always happen in practice, but a frequent Liberal Democrat complaint after the 2015 election was that that they couldn't get enough public credit for those occasions they forced a change in Conservative policy.
At its most basic, 'a confidence and supply' deal guarantees a minority government the support of another party when the House votes on motions of no confidence (and, before the Fixed-Term Parliaments Act, on supply bills, where a loss would also have effectively terminated the government's mandate). In theory, the second party could be in total, public, opposition to any other government bill. In this case, it appears the Conservatives and the DUP have agreed a small tranche of additional legislation where the Tories can expect DUP support, in exchange for support for certain DUP positions, and an estimated £1 billion of additional infrastructure funding being provided to the Northern Ireland executive.