Two arms-control agree-ments that would make it easier for the UK to gain access to American defence technologies are probably illegal under US law and should be halted, two powerful congressmen have argued in a letter to Donald Rumsfeld, US defence secretary.

One agreement, currently being negotiated by Pentagon and British officials, covers the highly sensitive bilateral work on ballistic missile defence, which has caused controversy in the UK because of government acquiescence to participating in the US-led programme.