Police could see the back doors of the lorry moving as the people inside knocked to be let out, the officer in charge of the investigation has said.
Somerset Area Superintendent Geoff Wessell spoke to ITV News:
More top news
After the heatwave come the storms, with lightning flashes illuminating the night sky across much of the country last night.
An Independence Day event at a UK base has been cancelled by the US Air Force over security fears.
British firms predict the economy should sustain a "solid" pace of growth for the rest of the year thanks to lower oil prices and inflation.