TF engine misfire

We have been trying to identify a random misfire on my MGTF VVC. we are using the testbook T4 diagnostic

The car will drive without any misfire for 10 minutes, or 20 minutes then start to misfire for about 100 metres with check engine light flashing then clear . The car has 53000klm on the clock and presents well. The car had been sitting for about 6 months when I bought it and the previous owner had disconnected the VVC unit because of this miss. He had been told that a new head and VVC unit was needed. But the car was still missing with it disconnected! I have reconnected the unit. I have changed/checked the following.

engine compression is OK but I cannot find the numbers for each cylinder. No oil in the water and no water in the oil.

Coil paks and leads
spark plugs NGK Grp 9
temp sens black offset pin Lucas MEK000030L
temp sens Blue straight pin Genuine MEK1000130L
thermostat (car was geting hot) PEL10016
physically checked the coil packs
ran T4 scanner check different channels and reprogram ECU
test fuel pressure

T4 error codes
P1300 misfire causing cat damage
P1316 misfire causing exc emmissions
P0300 Multiple misfire codes

Workshop now suspect ECU.
just noticed that neither O2 sensor were changed. But the upstream and downstream O2 sensors would trigger error codes on the T4. Or would they?

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TF engine misfire