Having progressed through the Saracens Academy Mercey began to take part in the main squad in the 2004–05 season, taking part in Saracens 'A' team sides.[3]
This progression continued in the following season when he became a full-time member of the Saracens squad while still part of the Academy system on 1 July 2005.[4]
The 2006–07 season saw Mercey make his Guinness Premiership debut and he went on to make four appearances, all from the replacements bench, and 13 first team appearances in all competitions.[5][6]
The 2007–08 season saw Mercey making regular first team appearances, including his first in a starting line up for a Guinness Premiership game.[5]
Mercey was injured throughout the first part of the 2012/13 season but his comeback coincided with an injury to Brian Mujati and therefore Mercey started several games in a row, not scoring but turning in some good performances.
In 2014 Mercey played as a replacement as Northampton beat Saracens to win the Premiership final.[8]
Mercey was first selected for England U19 duty a year ahead of many of his peers, which included four appearances in the 2005 IRB Under 19 World Championships[2] as well as outings in the 2004–05 U19 Six Nations.
Mercey was again called up for England U19 duty in the 2006 World Championships,[9] before once again taking a step up ahead of his peers to represent the Under 21 side at the 2006 IRB Under 21 World Championships featuring in winning sides against Fiji and Wales.[2][10]
At a national level he moved on from age group rugby to represent England Saxons in the Six Nations 'A' tournament, making his debut against Italy 'A' in February 2007.[2] His performance saw him soon in Saxons colours just two months later, as he appeared in every game in the Saxon's victorious 2007 Churchill Cup campaign.[2]
