Far-right Britain First is urging its supporters to join the Conservative Party in order to “make Boris Johnson’s leadership more secure”.
The extremist group, whose leaders were jailed last year, sent an email to subscribers claiming “thousands” of its activists were becoming members of the Tories.
It came after Mr Johnson was endorsed by Tommy Robinson and garnered public support from other far-right figures.
“If you haven’t joined the Conservative Party yet, we urge you to do so immediately, to make Boris Johnson’s leadership more secure,” Britain First said in an email sent on Wednesday.
“Senior Britain First officials and rank-and-file members have been receiving their Conservative membership cards in the post.