What does organic mean in UK with regard to poultry?
Chemicals are allowed- but they must be on the list prepared by "various organizations across UK and EU. The same holds for "otganic" vegetables, etc.

The poultry is allowed free range for at least a few hours. No requirement as to surface, may be gravel/sand or grass. The exposure to sunlight helps to provide sufficient vitamins A and D; which are added as supplements in confined conditions.

U. S. and Canadian requirements are similar.
Feed must be certified (no animal products, etc.). In Canada, use of hormones has been prohibited in all poultry since the 1960s; no hormones or antibiotics allowed in U. S.