About 500 former Wrightbus employees and their families have held a protest outside a church linked to millions of pounds in donations from the owners of the collapsed bus maker.

About 1,200 jobs were lost last week when the Ballymena-based producer of the Routemaster bus used in London went into administration. The Unite union has warned a further 1,700 jobs could be at risk in the engineering company’s supply chain.

Colin Graham, a Unite shop steward, said the former workers, wearing T-shirts saying “save our jobs” and banners emblazoned with the words “shameless greed” and “you reap what you sow”, were carrying out a peaceful protest amid heavy security including private guards employed by the Wright family.

He said the founder, Sir William Wright, who received applause as he arrived at the church, had told workers he was sorry about the way things had turned out.

Graham said: “We’re not here to shame the whole Wright family, we’re here to shame Jeff Wright alone.” Jeff Wright is the founder’s son and a major shareholder of Wright Group’s holding company.

The church in Ballymena, Northern Ireland, was able to expand thanks to donations from Wrightbus’s parent company. Photograph: Paul McErlane/The Guardian

The parent company of Wrightbus, Cornerstone Group, donated more than £16.1m to charity between 2012 and 2017. A proportion of these donations helped fund the expansion of Green Pastures, an evangelical church in Ballymena led by Jeff Wright.

The company also paid out £2m in dividends to shareholders, most of which went to Jeff Wright and a group called the Wright Evangelical Trust, over the five-year period.

In 2017, Cornerstone paid out £400,000 in dividends and £4.15m in charitable donations, despite making a £1.7m loss, compared with a profit of £10.8m the year before.

“How could he donate to the church without looking after the workforce and keeping the company going? That’s what we want answered,” Graham said.

The donations preceded increasing financial difficulties for Wrightbus, which made two rounds of redundancies last year, with 95 jobs going in February and June. These were despite recent sales successes, including a Transport for London order in May for 20 hydrogen-powered buses, each costing about £500,000 and only emitting water vapour.

Wrightbus went into administration after having cash flow problems and failing to find a new owner.

Protestors have made it clear they do not blame co-founder of Wrightbus, 92yo William Wright, for firm’s collapse. He was warmly applauded as he arrived at Church. pic.twitter.com/oPGUGgk9No — Mark Simpson (@BBCMarkSimpson) September 29, 2019

Administrators at Deloitte are continuing to seek a white knight investor. They are thought to have contacted a number of potential bidders who previously expressed interest in the company, including Jo Bamford, the son of the JCB billionaire tycoon Lord Bamford, the Northern Ireland businessman Darren Donnelly and the Chinese company Weichai, which is part of the state-owned conglomerate Shandong Heavy Industry.

Police in Northern Ireland have been investigating death threats against the Wright family. Jeff Wright said in a statement: “I am asking all elected representatives and those with influence in the community to help end this intimidation and fear.”