1 INTRODUCTION

2 OBSERVATIONS AND DATA REDUCTION
2.1 Observations
2.2 WFCAM data reduction
2.3 Source extraction and survey limits

3 SELECTION TECHNIQUE
3.1 Narrow-Band excess selection
3.2 Broad band colours: further selection, redshift confirmation and line contamination estimates
3.3 Spectroscopic comparison

4 RESULTS
4.1 Hα luminosity density at z=2.23
4.2 The properties of Hα emitters
4.3 Clustering of Hα emitters

5 SUMMARY