Diego Garcia Military Base and British Indian Ocean Territory Bill

Lord Hannay of Chiswick Excerpts

Report stage
Monday 5th January 2026 Lords Chamber

In general, my point applies, I hope, to a whole lot of amendments for which I would have much more sympathy—such as the amendment in the name of the noble and gallant Lord, Lord Craig. He makes a valid point, but his amendment says that that point would have to be explored with the Mauritius Government before the treaty could be ratified. Therefore, I am afraid, I cannot support it.

[Lord Hannay of Chiswick (CB)]

My Lords, I wish briefly to speak to Amendment 40 in the name of the noble Lord, Lord Callanan. I am struck by the fact that, in all his interventions so far in these debates—at Second Reading, in Committee and, now, on Report—he has never referred at all to the report of the International Agreements Committee on this treaty. He also seems not to have registered, let alone to respect, the vote that was taken at the end of the debate on 30 June.

The point I am making is that, were the noble Lord to go back to the documents and the evidence that was tabled at the time when the International Agreements Committee’s report was laid before this House, he would find there the testimony of Sir Christopher Greenwood. It is remarkably convincing and answers the question posed by the noble Lord in his Amendment 40; it describes what Sir Christopher thinks would happen in circumstances where Mauritius returned to a route that involved international litigation.

It is all set out there. He is an extremely distinguished British national judge of the International Court of Justice. It has nothing to do with the advisory opinion. It is to do with his views about the situation that would then exist. He believes that Mauritius would not have too much difficulty in convincing any international court to which it took litigation that the Chagos Islands were transferred at the time of Mauritian independence.

[The Minister of State, Foreign, Commonwealth and Development Office (Baroness Chapman of Darlington) (Lab)]

My Lords, I apologise to the noble and gallant Lord, Lord Craig of Radley, for not writing to him, but I hope that I can answer his concerns this afternoon.

Amendments 1 and 38, tabled by the noble and gallant Lord, relate to the termination of the treaty based on environmental degradation of Diego Garcia island. As I am sure that he will appreciate, given the importance of the base to both UK and US national security, we and the US are working hard to ensure that the base is protected from environmental damage. We have a programme to address coastal erosion and, while we cannot predict future erosion, specific studies have concluded that the overall land area of parts of the island that are not shaped by military construction decreased by less than a single percentage point over the last 50 years. However, I know that this is not really his point. He is using climate change and rising sea levels, but equally a significant pollution event, a meteor strike or something else could happen, so have the Government considered what they would do in an unpredicted and unpredictable situation that may arise and render the base unusable? That is the kernel of what he is getting at.

For obvious reasons, we do not want to get into a debate about other future hypothetical scenarios, whether they relate to the base becoming unusable or its no longer being needed. It is difficult to see that happening. The US, which has invested heavily in Diego Garcia, agrees that opening up the possibility of the agreement with Mauritius being terminated early is not helpful. However, I take the noble and gallant Lord’s point that, when dealing with a treaty over such a long period, we must at least be aware of the possibility that things can change. That is why we have included in the treaty the joint commission as a mechanism for agreeing between the UK, the US and Mauritius any developments relating to the base that we wish to raise. Should any of the hypothetical scenarios that I have referred to transpire, these are the sorts of issues that could be discussed in the joint commission, with decisions taken based on all the circumstances at the time. We have also included provision in the treaty for the matter to be raised up to prime ministerial level if necessary.

Using these mechanisms the UK and Mauritius would, in close consultation with the United States, agree a way forward. Ultimately, there is provision in the treaty for it to be terminated on two grounds, both of which depend on action by the UK. One is our failure to make payments. As noble Lords know, the UK abides by its international obligations, but in any particular case the Government of the day would need to consider their options in light of all the circumstances, looking at the terms of the treaty as well as wider international law. It is this wider international law, which we have not discussed previously, that I encourage the noble and gallant Lord to consider. He may wish to bear in mind that the international law of treaties permits the termination of a treaty when it becomes impossible for the treaty to be performed as a result of

“the permanent disappearance or destruction of an object indispensable for the execution of the treaty”.

That is wider international law; that is not something that is held within this treaty itself. That is helpful and I hope it reassures him about his concerns.

I hope that the noble and gallant Lord can see that we are taking steps that are necessary to prevent the base becoming unusable and that, however hard hypothetical situations might be for us to imagine today, there are processes in place established by the treaty to resolve them. Using these processes, based on the circumstances of the time, no doubt any future UK Government would do what was in the best interests of the UK.

In the same vein, Amendment 6 in the name of the noble Lord, Lord Callanan, discusses the ability to extend the agreement at the end of its initial 99 years. I assure him that there is already provision for the treaty to be extended by 40 years and beyond with the agreement of both parties. Even if agreement is not reached, the UK has the right of first refusal during that first 40 years after the initial period expires, meaning that no other country can use Diego Garcia without the UK being offered use first. I cannot accept his amendment as it seeks to change a carefully negotiated aspect of the treaty.

Similarly, I cannot accept Amendment 40, also tabled by the noble Lord, Lord Callanan, which calls on the Secretary of State to publish a statement of the Government’s understanding of the legal status of the Chagos Archipelago should the agreement be terminated. The noble Lord is aware that the UK honours its international obligations and is committed to the treaty. The grounds for terminating the treaty are incredibly limited, as I have said, and entirely depend on the UK’s actions.

I thought it might be helpful to the noble and gallant Lord, Lord Craig, in particular, to outline a little more detail about from the law of treaties, which I am relying on in my attempts to persuade him this afternoon. Article 61 of the Vienna Convention on the Law of Treaties, which the UK and Mauritius are both parties to, provides that:

“A party may invoke the impossibility of performing a treaty as a ground for terminating or withdrawing from it if the impossibility results from the permanent disappearance or destruction of an object indispensable for the execution of the treaty. If the impossibility is temporary, it may be invoked only as a ground for suspending the operation of the treaty.


Impossibility of performance may not be invoked by a party as a ground for terminating, withdrawing from or suspending the operation of a treaty if the impossibility is the result of a breach by that party either of an obligation under the treaty or of any other international obligation owed to any other party to the treaty”.


That covers the situation that he refers to—sea level rise—but would also cover many of the other situations that, at this stage, we are able to envisage occurring in the future.

I hope that noble Lords feel able to not press their amendments.