Which is true: 15% or 40% increase?

It is frequently stated that the UK’s Integrated Review of Security published in 2021 includes a plan to increase the number of nuclear warheads in the UK arsenal by over 40%. For example, see the references below to articles by Reuters and the Guardian.

However the UK government claims that the new stockpile ceiling of 260 is an increase of roughly 15% over the current ceiling.

Why this difference?

First we need to look at the data.

The UK Strategic Defence and Security Review 2010 said:

3.11 The Government has concluded that we can meet the minimum requirement of an effective and credible level of deterrence with a smaller nuclear weapons capability. We will therefore cut the maximum number of nuclear warheads onboard each deployed submarine from 48 to 40. Together with improved stockpile management, that will reduce our requirement for operationally available warheads from fewer than 160 to no more than 120. We will also reduce the number of operational missiles on the Vanguard class submarines to no more than eight. These changes will start to take effect over the next few years. This will enable us to reduce our overall nuclear warhead stockpile ceiling from not more than 225 to not more than 180 by the mid 2020s.

But it appears that the stockpile was not in fact reduced between 2010 and 2021 when the UK published its Integrated Review of Security which said:

In 2010 the Government stated an intent to reduce our overall nuclear warhead stockpile ceiling from not more than 225 to not more than 180 by the mid-2020s. However, in recognition of the evolving security environment, including the developing range of technological and doctrinal threats, this is no longer possible, and the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads.

Defending itself from accusations of increasing the number of nuclear warheads in the UK arsenal by over 40%, the UK government said:

The previous UK stockpile ceiling was 225, with a target to reduce to 180 by the mid-2020s. Such a reduction would likely only have been possible if the security environment had continued to improve, as we had seen when the target was introduced in 2010. The new stockpile ceiling is 260 which is an increase of 35 or roughly 15%. This is a ceiling not a target and is not the UK’s current stockpile.

What is the truth?

It is a matter of what you should compare with what.

The commonly held figure of over 40% increase comes from comparing the 2021 upper limit on the overall nuclear weapon stockpile of 260 with the 2010 target for the mid 2020s overall nuclear warhead stockpile ceiling of 180. This is an increase of 44.4%.

The UK government’s figure of 15% comes from comparing the 2021 upper limit on the overall nuclear weapon stockpile of 260 with the current UK stockpile ceiling which is still 225. This is an increase of 15.56%.

Who should we believe?

It would be true to say:

the current planned overall ceiling of nuclear weapons is a 44% increase over the ceiling planned in 2010.

One might consider that the fact that the 2010 ceiling was abandoned and the current ceiling is 225 warheads makes this hypothetical figure rather irrelevant.

And the widely quoted statements, such as those in the Guardian and Reuters and elsewhere, that Britain will expand its nuclear warhead stockpile by over 40%, are clearly not true. Experts believe the current UK nuclear weapons stockpile is approximately 225 warheads. See the article in Nuclear Notebook. The new ceiling is 260. If the UK reached that ceiling it would be an increase of 15%.

However, a 44% increase makes a good headline, which is what newspapers and opponents of nuclear weapons are looking for. Never mind the truth, just grab the reader’s attention.

References

Reuters: Britain to expand nuclear warhead stockpile by over 40% as global threats rise (https://www.reuters.com/article/uk-britain-politics-nuclear-weapons-idUSKBN2B81N4)

Guardian: Cap on Trident nuclear warhead stockpile to rise by more than 40% (https://www.theguardian.com/uk-news/2021/mar/15/cap-on-trident-nuclear-warhead-stockpile-to-rise-by-more-than-40)

UK Strategic Defence and Security Review 2010
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/62482/strategic-defence-security-review.pdf

UK Integrated Review of Security 2021:  https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/975077/Global_Britain_in_a_Competitive_Age-_the_Integrated_Review_of_Security__Defence__Development_and_Foreign_Policy.pdf

UK government claim of 15% increase: https://www.gov.uk/guidance/the-2021-integrated-review-nuclear-frequently-asked-questions

May 11 issue of Nuclear Notebook says current UK nuclear weapons stockpile is approximately 225 warheads: https://www.tandfonline.com/doi/full/10.1080/00963402.2021.1912309

UK government claims the increase in the stockpile ceiling is 15%: https://www.gov.uk/guidance/the-2021-integrated-review-nuclear-frequently-asked-questions