Gatwick would serve 15 domestic destinations if a second runway was built – up from 10 now.
New domestic points may include Dundee, Isle of Man, Liverpool, Londonderry and Nottingham, the airport said.
The increase in UK destinations would see an expanded Gatwick fly a total of 18 million passengers to and from London – one million more than a three runway Heathrow.
Gatwick says it already serves more UK destinations directly than Heathrow, where domestic services have been progressively cut back.
The suggested new UK routes came as Gatwick was rated as the preferred option over Heathrow for expansion, according to a YouGov poll of small and medium sized business leaders.
Stewart Wingate, chief executive of Gatwick, said: “An expanded Gatwick will deliver more competition and choice and, crucially, for businesses across the UK, it will have the dual benefit of better connectivity to London as well as a stronger network of airports around the country.
“A strong network of airports around the UK will provide cheaper airfares, more choice and better services for all travellers.
“A third runway at Heathrow, however, would restrict competition, reduce choice and connectivity, and restrict the growth of airports outside London,” he claimed.
“Expand Gatwick and the country gets two world-class gateways within a competitive network of airports and everyone will benefit from cheaper air fares through vigorous competition.”