Sir: There appears to be a point missing from the Euro-currency debate. Everyone assumes that there are only two scenarios to be debated: one, we do not wish to join and therefore do not; two, we do wish to join and therefore do so. May I suggest a third? We eventually decide we wish to join and we are vetoed by those who are already members of the euro- zone. What benefit would they gain from allowing the UK to join? It is not at all obvious now and it may be less so in five years.