There is a lack of consensus in the UK about the cost/benefit nature of nuclear energy, as well as ideological influence (for instance, those favouring 'energy security' generally arguing pro, while those worried about the 'environmental impact' against). Because of this, and a lack of a consistent energy policy in the UK since the mid-1990s, no new reactors have been built since Sizewell B in 1995. Costs have been a major influence to this (with Sizewell B having run at a cost of 6p/kWh for its first five years of operation), while the long lead-time between proposal and operation (at ten years or more) has put off many investors, especially with long-term considerations such as energy market regulation and nuclear waste remaining unresolved.