UK US tax treaty

[shotokan]

Dont do much international tax. I have an American client who lives in the UK. He receives an occupational pension and a Social security pension from the US. I'm aware that UK residents are taxable on worldwide income (subject to relief for any foreign tax paid) but looking at the tax treaty, I'm not convinced that he needs to declare these in the UK. That doesn't seem right though. Maybe I'm mis-interpreting what it says. Does anyone know what's right??

All comments are appreciated.