Lambda sensors info is only used in idle and cruise (PART THROTTLE) situations on something as old as that. Known as 'closed loop' operation where the feedback from the various sensors is used and the PCM tries to keep the AFR at Lambda 1 (14.7:1 AFR)

On full throttle the fuel system is in 'open loop' and AFRs will be lower (richer) for full power/torque and component protection.

If your car passes the MOT emission test and has no error codes relative to Lambda sensor, it should be working fine.