Table:
|  | 2019 | 2018 |
| --- | --- | --- |
|  | $ million | $ million |
| Current | 53.2 | 55.2 |
| Non-current | 13.6 | 14.4 |
|  | 66.8 | 69.6 |
Paragraphs:
25. Deferred income
The Group’s deferred income balances relate solely to revenue from contracts with customers.
Question:
What does the Group's deferred income balances relate to?