The group seeks to promote cooperation among those who would like, and could contribute to the Brexit movement to form a campaign ahead of the referendum.
The group’s joint statement cited by the BBC criticized Prime Minister David Cameron's negotiations with EU leaders, saying there was "…little if any indication that the government is even asking for significant reform or fundamental change."
In late May, the British government presented a bill on Britain's EU membership referendum to the parliament. The legislation would see a vote no later than December 31, 2017.
Earlier this month, almost 70 Labour lawmakers formed a pro-EU membership campaign group.
In the run-up to the UK May 7 general elections, the issue of Britain's European Union membership was high on the agenda.
After the election victory, British Prime Minister and Conservative Party leader David Cameron reiterated his intention to hold an EU membership referendum by the end of 2017.