I am currently a pre reg at KHP and they don't seem to have any bias between where people have studied! There are 10 of us at kings and we have come from 6 different universities and this is the same across all khp sites. The only one which does get preference are kings college students who can apply before pharmalife but I believe it is restricted how many pre regs go to them (there are 4 at kch).
You have to actually show that you have learnt from your experiences not just turned up. I had quite alot of hospital placements but alot of the other pre regs didn't have much. One of my friends at guys didn't have any hospital experience at the time of applying and still got her preferred programme.