Re: Gas Regs and windows in kitchen
Ventilation of some kind is necessary to be Gas Safe. That has to be an effective extraction over the hob, a suitable permanent air vent in the wall or an openable window. Ideally a combination of any two of the three options.
A Gas Safe engineer can suggest how best these options need be applied in your case. As it is a leased property your freeholder should be contacted and asked to rectify the situation as per Gas Safe advice.