Do not assume it is food residue when gas or combustion safety may be involved. Stop use and follow the appropriate emergency advice for gas smell or suspected fumes.
What the observation means
The smell's timing and location are useful once safe, but they are not a substitute for assessment. Carbon monoxide itself has no smell.
A useful next step
Call 0800 111 999 from a safe place for a gas emergency in Great Britain and follow instructions. Do not run the burner empty to identify the odour or mask it with ventilation while continuing to cook.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.