A couple of the CAA's GA Safety Sense leaflets will help. They're on the CAA website, but the site seems to be down at the moment. From memory, the ones you want are "Strip Sense" and (no surprise) "Performance".
Try
this link in a bit.
Edited to say that the Safety Sense Leaflets are in LASORS. The 2006 edition suffers from the same access problems from the CAA site as above,
but the 2004 edition is accessible. (Several Mb download).
The one you want for factors is Safety Sense Leaflet 7 - Aeroplane Performance:
However, you can go to the Horse's Mouth, since the Safety Factors contained in there are taken from
AIC 67/02 (Pink 36), as linked. Access to the AIS site requires free registration.
(Edited again because even I don't know what a "Horse's Moth" is...)