Do all rooms on the ground floor lead from the hall? What rooms are
there?
How large is the hall?

On the ground floor the Lounge and Kitchen lead off the hall. The
Hall is about 3m x 2m approx.

Some possible solutions:

1. Replace existing hall ionisation alarm with optical type and move away
from kitchen door, if at all possible. An optical alarm is less likely to be
set off by a few cooking fumes.

2. Remove hall alarm. Install heat sensed alarm in kitchen. Install
ionisation alarm in lounge.

The second solution probably doesn't quite match building regulations as
there would be no detector in the downstairs circulation space. However, in
my opinion it would be safer, as it would reduce false alarms, which are
dangerous, whilst still maintaining detection in all rooms likely to have
fires. A fire in the hall itself is unlikely and will set off your upstairs
detector in any case.

Christian.