The British sprinters both sustained a suspected broken pelvis, with Ellington also suffering a facial fracture and a broken leg in two places.
Ellington confirmed he will have an operation later on Tuesday.
He tweeted he had "been through some dark days" but said the procedure would be the start of his "road to recovery".
Both athletes were hit by a car on 17 January and will miss the 2017 season, which includes the World Championships in London in August.
A British Athletics statement read: "James Ellington and Nigel Levine have safely returned to the UK via air ambulance, following a road accident in Tenerife last week.
"Both athletes have been admitted to hospitals in London where they are receiving specialist medical treatment for their injuries, under the supervision of the British Athletics' medical team.
"Both James and Nigel have been overwhelmed by the support they have received since the accident last week."
