Talk to your local Environmental Agency or Town Hall Buildings departments, they have experience and can put you in touch with suppliers of ledge spikes, firms who will fit netting and other 'humane' solutions.

Sometimes a model of the pigeons natural enemy will work, but it has to be moved occasionally or they cease to react to it. Audio tapes of the enemy hunting calls played occasionally will also clear the area temporarily. There is no way to remove pigeons permanently.

Try to discourage residents from feeding them (not even the Mayor of London and all the borough councils can get that to work), and generally make their lives as miserable as possible. The numbers will lessen but I suspect that a pigeon is for life, not just for summer.

LTS