Stephen Morgan wrote to Hampshire's police and crime commissioner last month while still Portsmouth South MP before the election was called.
Mr Morgan wrote to Michael Lane after The News revealed the new system, which has spiralled in cost to £39m and is seven years in the making, cannot take a 999 call.
The Microsoft-designed platform, shared by Hampshire and Thames Valley police forces, will replace 20 systems.
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But the contact management platform could not take a 999 call - meaning the old system had to be used.
Mr Morgan said he had 'major concerns' over the cost and the emergency call capability.
In response, Mr Lane said the unit shared by both forces will be the first to use the CMP.
He said: ‘It has not been a simple journey to draw so many systems together and step forward into a digital environment that is modern and forward looking, but we are now very close to CMP being fully operational.
‘The Joint Operations Unit of Hampshire and Thames Valley will be the first in the country to benefit from this new type of command and control system.’
The system is being used for crime reporting.
CMP programme director Perry Shears said: ‘Until such time as the 999 calls are rolled into live, all current demand is being met through the legacy systems remaining available.
‘There is no impact to the current service being provided to the public.’