Britain would still have a healthy economy even if it left the European Union (EU), thanks to a "free trade" deal with its former partners, the economic spokesman for the UK's main Euroskeptic party told CNBC.

Nigel Farage's UK Independence Party (UKIP), which advocates immediate withdrawal from the EU, won the biggest proportion of the U.K. vote in this weekend's European parliamentary elections, beating more established parties to a 27.5 percent share.