1 INTRODUCTION

2 DATA AND SAMPLE SELECTION
2.1 The UKIDSS Ultra Deep Survey
2.2 Photometric Redshifts
2.3 Passive Sample

3 ENVIRONMENTAL MEASUREMENT

4 RESULTS
4.1 Red and Blue Environments
4.2 Colour-Density Relation

5 INVESTIGATING SOURCES OF ERROR
5.1 Cosmic Variance
5.2 Volume-Limited Sample
5.3 Monte Carlo Simulations

6 CONCLUSIONS