The Zionist Federation has refused to accept grassroots advocacy group Yachad as an affiliate member after claiming the organisation's day-to-day activities do not support Zionism - despite ZF chairman Paul Charney admitting in an email to Yachad that there were "no grounds" for vetoing its application.

Yachad had taken part in a 10-month-long process to join the ZF, which operates as an umbrella group for British Zionists and represents more than 120 other organisations.

ZF affiliate member organisations voted on Monday to reject the application. Mr Charney told Yachad director Hannah Weisfeld that "it simply went to vote, and the vote went against you".

Mr Charney later said that the ZF's affiliate members were concerned about Yachad's positions on settlement expansion and the boycott of products from Israeli settlements in the West Bank.

Groups wishing to join the ZF must be Zionist, "not just in theory, but in practice, day-to-day", he said. "Yachad's message on boycotting West Bank goods is not clear enough. People felt that was an issue. They are very unclear."

Yachad is explicit in its statements that it does not support the boycott of any Israeli products. It says in tandem that it opposes further investment in the West Bank.

Ms Weisfeld said Yachad members were shocked by the rejection: "We are a pro-Israel organisation right at the heart of the Anglo-Jewish community. We have thousands of members and work in dozens of synagogues and with hundreds of active members of youth movements.

"We are part of the Zionist discourse and want to be part of the continuing debate. There's no contradiction between us being who we are as an organisation and being part of the ZF. Zionism is not monolithic. We want our thousands of supporters to have a say in the debate."

Ms Weisfeld said the ZF "could not claim to be an umbrella organisation, but then decide what Zionism you are prepared to represent. It's about the people on the ZF deeming us and our Zionism as unsuitable".

During the lengthy application process, Yachad agreed to provide extensive details about its constitution, accounts, and willingness to adhere to the principles of the World Zionist Organisation.

ZF members spent the last two months studying Yachad activities. ZF representatives attended two Yachad events to gain a better understanding of the organisation and concluded that they had found "no strong reason at those events to reject the application".

Yachad informed its members of the decision on Wednesday, telling them: "The ZF doesn't represent you. Evidently it feels your Zionism is not good enough because you are a supporter of Yachad."

Supporters took to Twitter to complain, sending the ZF tweets with the hashtag #whatswrongwithmyzionism.

Defending the decision, Mr Charney said: "We are not obliged to include, or exclude, anyone else. We are not accountable to anyone else in this country. We are accountable to the World Zionist Organisation."

Charlie Gluckman, chair of Pro Zion, one of the largest constituent groups on the ZF national council, said he would call for a re-vote.

Rabbi Danny Rich, chief executive of Liberal Judaism and a ZF patron, said: "I'm surprised in one sense since Yachad is a respectable Zionist organisation and I can see no reason why it would not be suitable for membership. But bearing in mind the campaign there was to remove me as a trustee of the ZF, nothing the organisation does any longer surprises me."

Mick Davis, chair of the Jewish Leadership Council trustees and UJIA honorary president, said: "All those who believe that Israel is the nation state of the Jewish people and who fight for its legitimacy are Zionists irrespective of their views on specific policies of different Israeli governments.

"The Zionist family is a big tent that should welcome all who subscribe to those values. Yachad is clearly in that camp even if some, including myself, may not agree with all of their positions. Yachad's track record in publicly opposing boycott, divestment and sanctions on campus is firm evidence of those credentials."

Board of Deputies president Vivian Wineman said: "We regard Yachad as an important part of the Zionist movement. They were involved in the Big Tent in Manchester and will be involved in the Closer for Israel rally in June. We are proud to have them involved."

Matt Plen, chief executive of Masorti Judaism, said: "We believe that the representation of a wide range of views within the ZF in support of Israel can only lead to a more balanced perspective on the many issues Israel faces."

The Movement for Reform Judaism said it supported the work of the ZF as "as the united body of British Jewish communities in support of Israel", but added: "We strongly disagree with the exclusion of Yachad, an organisation actively reflecting the will of UK Jewry for a two-state solution."