"Today is more than a transition. Today is an opportunity to rejuvenate our transatlantic relationship, which has greatly suffered in the last four years. In these years, the world has grown more complex, less stable and less predictable".
The dollar index recovered on the day and was last up 0.2pc just short of 90, but remained on track for a fall of 1pc over the week. It had reached its lowest in more than two years at 89.723 on Thursday.
"The prime minister will leave no stone unturned in this process, but he is absolutely clear: any agreement must be fair and respect the fundamental position that the UK will be a sovereign nation in three weeks' time," the source said.