Shadow Foreign Secretary Douglas Alexander said:
On the same day that top British business leaders fired a warning shot across the bows of the Prime Minister, a senior White House official has also signalled concerns about the possibility of Britain leaving the EU.
There is today a real risk of Britain sleepwalking towards exit because of a Prime Minister motivated more by the need for party unity than by the interests of the country.
More top news
Rescue workers are at the site Sunday morning trying to cut open mangled coaches.
Despite chilly temperatures it will be a mostly dry day, and milder than yesterday.
The Sunday Times alleges a missile malfunctioned after launch during a routine test of the UK's nuclear deterrent last year.