73% is likely % of families in uk with at least one car, attached is Worldbank data.
The 3 in the other report is probably a typo
http://www.nationmaster.com/graph-T/tra_car
Country Description Amount
1. Italy 539 per 1,000 people
2. Germany 508 per 1,000 people
3. Austria 495 per 1,000 people
4. Switzerland 486 per 1,000 people
5. Australia 485 per 1,000 people
6. New Zealand 481 per 1,000 people
7. United States 478 per 1,000 people
8. France 469 per 1,000 people
9. Canada 459 per 1,000 people
10. Belgium 448 per 1,000 people
11. Sweden 437 per 1,000 people
12. Norway 407 per 1,000 people
13. Finland 403 per 1,000 people
14. Japan 395 per 1,000 people
15. Netherlands 383 per 1,000 people
16. United Kingdom 373 per 1,000 people
17. Denmark 353 per 1,000 people
18. Ireland 272 per 1,000 people
Weighted Average 458.1 per 1,000 people