The Government did not necessarily wish to be bound by EC measures on visas, asylum and immigration and negotiated a Protocol to the UK the necessary flexibility. The effect of this Protocol is that the UK does not take part in the negation and adoption of such measures and is not bound by them, unless within three months of a proposal for legislation being presented to the Council the UK notifies the President of the Council that ‘it wishes to take part in the adoption and application’ of the proposed measure. This is the UK opt-in. No thought seems to have been given when the Protocol was drafted to what the situation might be if such a measure came to be amended by further legislation. What if the UK had opted in to the first, but did not wish to opt in to the second? Or vice versa?. A further problem, arises when changes need to made to related measures, some of which apply to the UK, some which do not. For example, codification. This report looks at these and related issues concerning the UK opt in.