to update, fitted a new cat and it passed its mot, next day however the MIL came on and got the following codes

P1166 Primary HO2S (No. 1) Heater System Electrical
P1167 Primary HO2S (No. 1) Heater System
P0136 Oxygen O2 Sensor Circuit Low Voltage (Bank 1, Sensor 2)
P0138 Oxygen O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)

the MIL was not on before the new cat was fitted, i tried to richen the mixture by blocking the air intake, tried to weaken it by removing the air trunking, it all does nothing, voltage stays at 0.8v, checked the lambda is getting the heated and its getting 12v on the engine loom side.

at wits end now.