London's mayor Ken Livingstone has accused a leading sculptor of creating an art work that looks like "a large pile of dog mess".
The Nelson Mandela statue was created by Ian Walter
The attack came after artist Glynn Williams' criticised a statue the mayor wants sited in Trafalgar Square.
Westminster Council opposes the mayor's proposal and called Mr Williams to give evidence at a planning inquiry into it.
Its refusal of an application to site a 9ft Nelson Mandela statue on the north terrace, sparked the inquiry.
Mr Williams told the inquiry that the £400,000 Mandela statue, created by sculptor Ian Walters, was "run-of-the-mill mediocre modelling".
He also said a more original and inventive sculptor should have been chosen to create it.
Mr Walters work had previously been chosen over Mr Williams' to be exhibited outside Huddersfield train station.
The mayor held up two photographs of Mr Williams' sculpture of Harold Wilson as he made the comments outside the three-day inquiry.
He said: "The only sense that it looks like Harold Wilson is if Harold Wilson has been dead for several days and has started to decompose and is emerging out of a large pile of dog mess.
"It is all very well for people with fine arts degrees but for ordinary people like myself we want a statue to look like the person."
Westminster Council refused planning permission for the Mandela statue on the grounds it would "clutter" the space, fill too prominent a position and harm protected views of the National Gallery and St Martin-in-the-Fields church.
It also said the statue would be an obstruction when the square is used for large events and would therefore be better placed on the square's east side outside South Africa House.
A decision by the Office of the Deputy Prime Minister is expected at the end of October.