As most tests don't say whether it was driver with or without a passenger I think we should accept the fastest times otherwise we risk invalidating half the lap times on this site.
In such a light car as the Caparo the difference is more obvious but for most "normal" cars the impact should be minimal.
The more limitations we put around lap times the more difficult we make it for people to post up new times..... ie. car must be stock, no tuned car, only road legal cars, only road legal tyres..... perhaps just add a notation somewhere IF we know whether it was 1 up or 2 up but allow any times that we have?...... Many people would like to see the difference between 1 up and 2 up for cars like the Caparo.....