When inserting or removing an internal wall, care should be taken not to make ventilation worse. Any new kitchen or utility room should be provided with a mechanical extract fan.
The type of room will determine how much ventilation is required. Part F of the building regulations says that where a kitchen previously had only a recirculating fan this can be retained or replaced if it is made no worse.
However, to minimise condensation, an extractor sending air externally is preferable.
In a kitchen and utility room it will need to extract 30 litres per second if over a hob and 60 litres if placed elsewhere.