London Mayor Boris Johnson has stepped into the row over British National Party leader Nick Griffin attending one of the Queen’s three Buckingham Palace garden parties in July.

The London Assembly’s 25 members are traditionally invited to one of the parties. Richard Barnbrook, the BNP’s London Assembly member, has said he will take Mr Griffin to the party on July 21, the last of the three parties.

Now Mr Johnson has written to LA leader Darren Johnson asking him to persuade Mr Barnbrook to take another or have the invitation taken away.

The Mayor said in his letter that the attendance of Mr Griffin or another prominent member of the party threatened “to turn a happy annual event - at which thousands of people across the country are acknowledged for their service to the community - into a political stunt.

We cannot tolerate any such abuse of the invitation or any potential embarrassment to Her Majesty. I am therefore writing to call on you to inform Mr Barnbrook -at the earliest opportunity- that he must either bring a guest who will not provoke political controversy, or consider his invitation rescinded.”

An aide of the BNP’s London Assembly member Richard Barnbrook said earlier in the week that he had received an e-mail inviting him to the party.

But a spokesman at Buckingham Palace said formal invitations had yet to be sent out.

“No invitations to this year’s garden parties have yet been issued,” said the spokesman.

“The Greater London Assembly is one of more than 1000 organisations given allocations for garden parties. The Queen does not scrutinise and is not consulted on the list of accompanying guest names as they are official, not personal, invitations.

As such, Buckingham Palace relies entirely on the nominating organisations.

“Where a guest is not judged to be a direct threat to security by the police, an invitation would be issued.”

The JC understands that 25 pairs of tickets have been sent to the London Assembly, which has 25 members. But it was up to the Assembly to decide whether the tickets would go entirely to the members or whether they would be shared between members and administrative staff.

Once people have received the initial indication, they must submit proof of identity and fill in a security form which is checked by police before the formal invitations are sent out. Guests are then checked by police before entering the Buckingham Palace gardens.

Ruth Smeeth, of the Board of Deputies-backed “Your Voice or Theirs” campaign to prevent the BNP winning seats at the European elections on June 4, said: “Nick Griffin still denies the Holocaust. He also has a conviction for incitement to racial hatred. It is very disturbing to think of him being welcomed by the Queen.

“This makes it even more important that everyone uses their vote in the European elections. If the BNP is successful and wins a seat, we can expect to see more of this in the future.”