Donald Trump's praise of US-UK relations appears to be out of step with reality.

The US president has used a state visit to London, to call the relationship the greatest alliance the world has ever known.

He's also promised Britain a new trade agreement if it follows through on leaving the EU.

London University international relations expert Rob Singh says [told Mike Hosking] in reality, the US and UK are actually drifting apart.

"We're not really a reliable ally militarily, Huawei thing on intelligence is a problem, diplomatically, we just don't see things like climate change and Iran the same way."

That gap has been seen through the reaction to the trade deal, which has been met with extreme trepidation in the UK.

Singh says Britons are fearful of America pushing through a one-sided agreement.

"Everyone here is incredibly frightened that they will be extremely predatory, particularly on the National Health Service, with pharmaceutical companies taking over."

Singh says the agreement could also force Britain to abandon its current food safety laws.