The Church of England has invested up to £10m in one of the world's major arms firms, which supplies systems and technology for unmanned drones and jets to conflicts around the world. The discovery, on the eve of what is set to be the biggest day of protests against DSEi – the UK's leading arms fair – in Docklands, London, tomorrow, has led worshippers to accuse church leaders of profiting from conflict.

The Church Commissioners and Church of England Pensions Board are both shareholders in General Electric (GE), with shareholdings up to £10m. Yesterday, the Church defended the investment, claiming less than 3 per cent of GE's business was based in arms sales.

But the firm, along with its key subsidiary General Aviation, is a leading supplier of "integrated systems and technologies" for combat aircraft, military transport, helicopters, land vehicles and unmanned aerial vehicles – better known as drones.

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It is the 20th-highest-ranking firm in the world when it comes to defence sales, which accounted for almost 3 per cent of its total revenue last year – an estimated $4bn.

GE also makes the F101 aircraft, which took part in combat in Afghanistan and Iraq. Designed as a "strategic nuclear bomber", it was modified to carry a "diverse range of conventional weapons", according to GE's website.

While the Church of England is not breaching its own rules by investing in the firm – investments in companies that derive less than 10 per cent of turnover from strategic military sales are allowed – some church members reacted angrily to the news.

Keith Hebden, an Anglican priest who was arrested earlier this year for breaking into RAF Waddington – from where drones used in Afghanistan are remotely controlled – said the Church of England's policy was wrong. He explained: "We're going to end up with problems. This means we have a stake in wanting there to be war."

Symon Hill, co-founder of the anti-cuts campaign group Christianity Uncut, said: "Investments in GE conform to the letter but not the spirit of the Church of England's investment policy."

A Church spokeswoman pointed out that GE produces dishwashers, lighting, aircraft engines and power plants. She added: "Some of GE's engines and other products are supplied for military planes, boats and land vehicles. Our research provider estimates that less than 3 per cent of GE's turnover comes from strategic military supplies."

The Campaign Against Arms Trade added: "GE is undoubtedly an arms company – why else would it be exhibiting its wares at one of the world's largest arms fairs? If the Church is committed to following an ethical investment policy, it should drop the GE shares from its portfolio and invest it in companies producing more ethical and beneficial products, including renewable energy technologies."

Today's revelations come months after the Church admitted it invested in funds that provided money for the Wonga payday loans company. The Archbishop of Canterbury, Justin Welby, had previously said he would try to force the firm out of business by helping credit unions compete with it. He wanted the Church's investment rules to be reviewed following the row.