Campaign group Fathers4Justice is claiming its members have defaced a painting of The Queen at Westminster Abbey.
The painting, by artist Ralph Heimans, had been on display in the Chapter House for a few weeks before it was vandalised with paint.
An Abbey spokesman confirmed the picture had been removed from public view, and Scotland Yard said a 41-year-old man had been arrested on suspicion of criminal damage.
It was unveiled in London last year for the Queen's Diamond Jubilee celebrations.
BREAKING NEWS: Two Fathers4Justice protestors arrested after incident at Westminster Abbey at portrait of the... fb.me/Xov6EI3B— Fathers4Justice (@F4JOfficial) June 13, 2013
An image was then posted on the Fathers4Justice Facebook page, with the caption: "This is not an official F4J protest but we understand these are members of F4J."
An Abbey spokesman said: "In an incident at lunchtime today, a visitor to the Abbey sprayed paint on the Ralph Heimans portrait of the Queen presently on display in the Chapter House.
"Until work can be done to remedy the damage it will, very regrettably, not be possible to have the painting on public view."