In an established parliament any proposal for the allocation of seats will affect sitting members and their parties and is therefore likely to be evaluated by incumbents in terms of its effects on the seats that they hold. This paper evaluates the Cambridge Compromise’s formula in relation to compromises between big and small states that have characterised the EU since its foundation. It also evaluates the formula by the degree to which the Compromise departs from normative standards of equality among citizens and its distribution of seats creates more anxiety about the risks of losses as against hypothetical gains. These political criteria explain the objections to the Cambridge Compromise. However, the pressure to change the allocation of seats is continuing with EU enlargement and the arbitrary ceiling of 751 seats imposed by the Lisbon Treaty.