It seemed such a good idea at the time – a dignified event to mark the life of one of Britain’s greatest engineers, designer of a much-loved transport icon. But now the event is threatening to unleash an undignified battle involving superglue and rubber ducks.

A statue of Sir Nigel Gresley is due to be unveiled in April, marking the 75th anniversary of the death of the designer of the Mallard steam engine. But there is a risk that his achievements will be eclipsed by an arcane dispute that started in the letters pages of local and national newspapers and quickly escalated on social media.

At the heart of the row is the decision by the Gresley Society to drop its commitment for the statue’s original design to include a mallard at Sir Nigel’s feet. Campaigners are plotting to make their own avian additions when the 7ft-high bronze of Gresley, commissioned from sculptor Hazel Reeves, is unveiled at London’s King’s Cross station on 5 April.

The news has dismayed the Gresley Society, which fears that the protest will overshadow what is meant to be a celebration of one of the great designers.

With a top speed of 126mph, the Mallard holds the record for being the fastest steam locomotive in the world. Another Gresley design, the Flying Scotsman, is an enduring achievement.

When applying for planning permission, the society’s trust stated: “This duck is no mere whimsy. It is an allusion to Sir Nigel’s most famous locomotive, the Mallard, which holds the world speed record for steam locomotives. It is also an allusion to Sir Nigel’s habit of feeding mallards at his prewar home in Salisbury Hall.”

But last year, the society announced it had decided to remove the mallard following “widespread consultation”. It is understood that two of Gresley’s grandsons believed the addition of the duck was demeaning.

The volte-face provoked anger on Facebook and Twitter. Supporters of the duck argued its addition would pique the curiosity of passers-by and encourage them to learn more about Gresley.

“Which is the statue that you are going to take your grandchildren to see?” asked broadcaster Vanessa Feltz. “Which is the statue that you will make a pilgrimage to see; which is the statue that you will take a picture of yourself next to: the one with the duck or the one without it? I’m 100% pro-duck.”

However, after a special meeting of the society’s council, the outcome “was a unanimous decision, with two abstentions, to delete the mallard”. Three Gresley Society council members resigned in protest and the duck lobby cried foul. Now they are hitting back.

In a letter to the Camden New Journal, Libby Ranzetta, a leading member of the pro-duck faction, Gresleyduck.org, has warned the society its decision to pull the duck will have consequences.

“Planning permission was granted in 2014, after public consultation, for man and duck, yet the Gresley Society has been given the all-clear by Camden to omit the mallard without fear of redress from the council’s enforcement officers,” Ranzetta writes. “I wonder if this laxity might be a cause of regret when people start leaving their own duckish tributes at Sir Nigel’s feet, as they surely will if the mallard is left out.”

Ranzetta told the Observer: “I can’t condone the placing of tribute ducks near Sir Nigel’s feet because that really will detract from the dignity of the statue but, to be honest, a little part of me would be delighted to see them there in perpetuity. They’d certainly bring attention to Gresley and his achievements – and annoy the hell out of the po-faced philistines who run the Gresley Society.”

The pro-duck camp has posted images on social media of the rubber ducks, duck balloons and chocolate figurines they plan to place at Sir Nigel’s feet. One member of the camp has pledged: “I’m going to stand there all day every day in a Donald Duck costume because they’ve annoyed me so much.”

Nigel Harris, editor of Rail magazine, has expressed concerns about how the tributes will be secured. “Superglue chaos will be a problem,” he tweeted. “Doing the right thing often isn’t easy: GS pls take note.”

But Gresley Society chairman David McIntosh dismissed the actions of the pro-duck rebel alliance. “They threatened to turn up at our AGM in a duck costume but didn’t, so I’ll treat it with the same degree of seriousness,” he said. “These people have got only a loose connection with reality. The make all sorts of idle threats. They call us Nazis, all because they can’t win a vote.”

McIntosh said that almost every one of the 130 people who had donated to the statue fund was happy with the outcome of the vote to jettison the mallard.

“We made the offer that anybody who felt upset by the deletion of the duck could have their money back and only one subscriber did. It shows our stance is supported by our members and supporters. A campaign by people on Facebook by people who have no connection or involvement, well, we don’t regard that as significant or of any real importance.”

Sir Nigel’s statue was cast last week at the Bell Foundry in London’s East End. There was no duck.

Engine master

Sir Nigel Gresley (1876-1941) is described by the Gresley Society as “a mechanical engineer of great skill [who] had the imagination and boldness to innovate, a flair to organise and to lead, an artist’s eye for line and proportion, and a touch of showmanship”.

In a career during which he worked for the Great Northern Railway and the London and North Eastern Railway, he designed some of the most famous steam locomotives in Britain, including the LNER Class A1 and LNER Class A4 Pacific engines.

On 30 November 1934 his Flying Scotsman, an A1 Pacific, was the first steam locomotive to officially exceed 100mph in passenger service, a speed exceeded by the A4 Mallard on 3 July 1938 at 126mph, a record that still stands.