Divisions that may spell the end of the far right British National party exploded into the open on Tuesday with the departure of one of its two MEPs.

Andrew Brons announced he was quitting the BNP with an angry statement claiming that up to 90% of the party's membership, activists and former officials had already left. He blamed the party chairman, Nick Griffin, for "having destroyed the party of which he is still nominally head".

"Over the last 16 or 18 months, I have been marginalised to such an extent in what is left of the British National party that I have been expelled in all but name," said Brons, who plans to remain MEP for Yorkshire and the Humber.

Observers of the British far right predict Brons will launch a new party in competition with the BNP.

Nick Lowles, director of Hope Not Hate, wrote in a blog that four parliamentary byelections coming up in the next few weeks offer Brons's supporters a chance to flex their muscles, and that his new party would almost certainly contest Croydon and Middlesbrough.

Brons claimed that Griffin, who represents the North West England constituency in the European parliament and is now the BNP's sole MEP, had "described him in a text to his attack dogs as 'vermin'".

"More recently, he described me as a 'state agent' – a description he attached to me 26 years ago, but which obviously did not apply when he appointed me as the lead candidate in Yorkshire for the European elections," he added.

Chris Beverley, a former BNP member, has remained as a personal assistant to Brons after leaving the party and joining the English Democrats. However, Brons is not expected to follow suit.

Brons has been distancing himself from Griffin for some time and last year appeared to back an unsuccessful leadership challenge by Richard Edmonds, prompting speculation that he was preparing to lead a breakaway group.

Griffin has been under growing pressure since the BNP's poor showing in 2010's general and council elections, when it lost all but two of the 28 councillors up for re-election and was wiped out in what was then its east London stronghold of Barking and Dagenham.

Brons became the BNP's first MEP in 2009 after receiving 120,139 votes in the Yorkshire and Humber region. He was a teenager when he started his political activism in the mid 1960s, joining the neo-Nazi National Socialist Movement.

By the 1970s, he had moved on to the National Front, then the leading far-right group in Britain. He was voted on to the NF's national directorate in 1974 and, as the NF's education officer, he hosted seminars on racial nationalism and tried to give its racism a more scientific basis.