Given that the death penalty had already effectively been abolished in the UK decades previously (in 1969 in Great Britain and in 1973 in Northern Ireland), it was uncontroversial in politics to sign the two protocols of the European Convention of Human Rights that prohibit executions in peacetime (protocol 6, signed in 1999) and in all circumstances (protocol 13, in 2002). (That it might be controversial among the public is currently being tested by petitions, which this blog wrote about here.)
This website generally objects to the way in which international treaties can impose legal obligations upon the UK with the agreement of the government but not of parliament. It is essential that EU treaties are ratified by the House of Commons, for example. The UK’s ratification of the two protocols against the death penalty followed their notification to parliament and the absence of objection (the so-called Ponsonby Rule).
There are two effects of adopting international treaties that confirm existing domestic practice. First, it strengthens the credibility of the government if it is to argue that other countries should do what we have already done. Secondly, it makes it harder to change that existing domestic practice in the future.
It would be open to the British parliament to reinstate the death penalty but it would have to withdraw from or renegotiate a number of treaties first. The protocols of the ECHR mentioned above would have to go, as would at least part (and possibly all) of our EU membership, and there would be implications for extradition and possibly other treaties too. So we could do it, but it would not be easy and it would not be free of wider consequences.
To make it harder to change an existing domestic practice acts as a brake on public opinion. Are we really sure we want to do something? It is not anti-democratic to submit to an international system of some sort if we can democratically choose to withdraw from it.
The psychologist Dan Ariely has proposed a self-control credit card to which the holder can choose to apply overall budget limits (no more than £X can be spent each month) or individual budget limits (no more than £X on shoes, say) or limits of other kinds (no downloading music after 10 pm). Each of these rules is optional, but they make it easier for the individual to stick to defined goals.
Membership of the EU provides a form of self-control for democracy and human rights. We don’t have to have it, but we are much better off with it.