DC3 Dave, Both LCY and SEN have London on their doorstep and London in their name. It serves not only the 9m residents but also the countless inbound business travellers (LCY) and leisure traffic. No marketing campaign will ever be able to position SOU as an alternative to the London area and certainly not to people coming in from overseas.
SOU is here to serve Southampton & the immediate region. Does it have a big enough wealthy catchment to emulate LCY?