Looking at peak summer (August 2020) here are the base sizes (not including standby aircraft):
Note: Base sizes vary throughout the summer period - EDI/DUB see long haul flights etc
Manchester has the most short haul flying whereas LGW has the most long haul flying
MAN - 18 (11x B738, 1x B752, 2x B763 and 3/4x B787) B787 operates mostly long haul, however schedule keeps updating!
LGW - 16 (8x B738 (4x op by Norwegian), 2x B752 and 6x B787) roughly 3x B787 operate long haul and 3x short haul
BHX - 10 (7x B738, 2x B752 and 1x B787) B787 operates long haul 7x days a week plus a second visits for another 2x days a week
BRS - 7 (5x B738, 1x B752 and 1x B787) B787 operates long haul 4x days a week and short haul 3x days a week
NCL - 4 (4x B738) plus B787 operating long haul between 2 and 5 days a week
DSA - 4 (4x B738) plus B787 operating long haul 2 days a week
GLA - 3 (3x B738) plus B787 operating long haul between 2 and 5 days a week
EMA - 3 (3x B738)
CWL - 3 (3x B738)
STN - 2 (2x B738)
DUB - 2 (2x B738)
EXT - 1.5 (1.5x B738 - 2nd aircraft based Mon-Thu)
BOH - 1.5 (1.5x B738 - 2nd aircraft based Fri-Sun)
BFS - 1 (1x B738)
EDI - 1 (1x B738)
LTN - 1 (1x B738)
NWI - 1 (1x B738)
ABZ - 1 (1x B738)