Thanks !, that's interesting. I have a another trip to the US in August, does this mean they will assume I have remained in the US from point of entry in July to point of re-entry in August? Would have thought that they would know when I left the country; I am only planning on staying in US one day.

I am happy to pay a $6 fee to enter, I just want to make sure the visa waiver programme applies to a UK national crossing from Canada to US. I am worried that if I am refused entry due to not having appropriate paperwork that I may have to apply for a visa when I come back in August via JFK.