The would be 'referendum' under the last labour government was with regards to adopting the proposed EU consitution, which would have required ratification by popular referendum of all EU member states.

As, by May And June 2005 the constitution was reject by Netherlands and France, the whole ratification process was brought to an end. To stil go ahead with the referendum would have been a pointless waste of money as by that point the result wou;ld have bean irrelavant. It would be like holding a referendum tomorrow on the 2010 Equalities Act which is already law. Labour has not promised at in-out referendum since 1975.