Is there cyclocross/xc/enduro/downhill/gate racing?
Enduro-
QECP Day & Night Enduro in May
QECP Trail Collective Enduro in July
DH-
Gravity project, 5 race series in Hampshire (GP1, GP2 ,Rogate & QECP)
PORC, 5 race series in Kent
Bull Track, 3 race Series in East Sussex
And both Tidworth and Aston Hill both have races but are a bit of a drive.
XC & CX-
Not sure apart from the Brighton big dog & the Southern XC series.