which it uses in its Reference Scenario but it says

A critical uncertainty is whether the substantial investments needed in the upstream hydrocarbons sector in MENA countries will, in fact, be forthcoming.

They then go on to give a Deferred Investment Scenario to examine what would happen if this investment were not forthcoming and investment stays at a constant percentage of GDP.

Lower investment on this scale causes MENA oil production to drop by almost a third by 2030 compared with the Reference Scenario. Production falls further than investment by the end of the projection period because of the cumulative effect over the projection period. In 2030, total MENA output reaches 35 mb/d, compared with 50 mb/d in the Reference Scenario. Saudi Arabia's production, at 14 mb/d in 2030, is more than 4 mb/d lower than in the Reference Scenario. MENA's share of world oil production drops from 35% in 2004 to 33% in 2030 (against a rise to 44% in the Reference Scenario).

As a idea of the size of this investment, $17 trillion is equal to the total value of 8 years of world production of oil at its present production rate at $70/barrel to be invested over 25 years. Since a fair part of this investment will be in the form of energy costs the growth in net energy available after such investment will be substantially curtailed.

It was suggested earlier on TOD (I can't find the reference) that the IEA was hinting that the Reference Scenario was not to be taken seriously and rather than admit that their previous rosy projections had been wildly out had decided to leave these in the Reference Scenario and put the more realistic projection in the alternative scenario. That way they can blame the producers for failing to meet their investment obligations rather than their poor forecasting.

If this is their intention it seems it was too subtle for the UK government.