Around 43% of departmental expenditure limits are ring-fenced. As a consequence, public expenditure control - on the scale required to address the deficit - will be increasingly difficult. While ring-fencing reflects public priorities, those preferences are not equally strongly held for all ring-fenced areas. Support for the 33.5% cumulative real increase in aid over the course of this Parliament, for example, appears to be lower than for health and schools. The Committee also remains concerned about the impact of the Government's Help to Buy: Mortgage guarantee scheme. An abrupt end to the scheme could distort the market, as could announcements which radically alter people's expectations. Forecasts of additional revenue from many anti-avoidance measures are inherently extremely uncertain. The Committee warned in its report on the Autumn Statement 2012 that the forecast revenues from the UK-Swiss agreement - at £5.3 billion - were subject to uncertainty and that the proceeds may not meet expectations. These concerns appear to have been justified. Even after the event it is often very difficult to establish how much a particular measure has raised. The OBR should look again at how the Government accounts for projected revenues, based on previous experience. Even after the event it is often very difficult to establish how much a particular measure has raised. The more transparency about the yield, and therefore each proposal's effectiveness, the better