A leading fracking firm is to start drilling on the former site of a huge explosive factory, in a decision described as "beyond comprehension" by the local MP.

Dart Energy, which is expected to begin drilling this weekend, says the site is "absolutely" safe. But opponents say there is a risk of unexploded bombs and that safety tests have not yet been completed. The revelations add to concerns about the regulation of "unconventional" gas exploration in the UK, which has seen deformed wells go unreported, planning rules breached and trespassing.

The 500-acre Royal Ordnance Factory Ranskill, near Daneshill Lakes in Nottinghamshire, was one of three built to produce cordite during world war two. Another explosive, RDX, was produced after the war and the site was broken up in 1975 and is now mostly woodland and farmland.

The original planning statement submitted for work on the site claimed "there are no recorded past workings on the site". Dart Energy, which is working with oil giant Total to exploit shale gas reserves elsewhere in the UK, says it does not intend to frack at the Daneshill site but wants to use another unconventional technique to extract gas from coal deposits.

"It is beyond comprehension that you would chose a former ordnance site for your first drilling site," said John Mann, Labour MP for Bassetlaw. He told the Guardian: "There needs to be a proper investigation of the risks of drilling on the munitions site and that has not been done. All the authorities are passing the buck on this."

The presence of the former explosives factory was raised with Nottinghamshire council and the Environment Agency by local people. Chris Crean, Friends of the Earth Midlands campaigner, said: "David Cameron and his fracking pals keep telling us that the UK's regulatory framework means fracking and other extreme energy developments won't harm people or the environment. But this fiasco makes it clear that it's not as safe as they want us to believe. It suggests serious weaknesses in the regulatory regime when the authorities are relying on local residents to identify the issues they should be investigating."

An Environment Agency (EA) technical report on the contamination of Ministry of Defence (MoD) land states: "As most MoD sites that operated during the war were military targets, there is often an issue of unexploded ordnance." It also notes recordkeeping was often poor in wartime.

A spokesman for the EA said Dart held all the permits it needed, but added: "We have requested soil samples to provide conclusive proof that there are no residual explosives on site." Crean said: "We think it's irresponsible for Dart to start to drill before they and the regulators know what the results of the soil analysis are."

"Nottinghamshire council has reviewed the evidence available and discussed the matter with other agencies and concludes that, whilst with all developments there is always a risk, that in this case the risk is low," said an council spokesman.

A Dart Energy spokesman told the Guardian: "The drill site is very small, about half the size of a football pitch and is located on a previously undeveloped part of the Ranskill Royal Ordnance Factory (ROF) site. While the drill site is clearly located within the former ROF Ranskill curtilage, available aerial photos and historical Ordnance Survey mapping indicates that the majority of the manufacturing infrastructure, and therefore sources of potential contamination, are in fact located some 1km to the north of the well pad."

He added: "The intrusive site investigation did not encounter any significant made ground, demolition rubble or other potential indicators of contamination on site." Aerial photos seen by the Guardian record the presence of "rolling houses", "paste drying" and "horizontal presses" within metres of the drill site.

Earlier in 2014, Dart Energy had to halt work at the site after it breached the terms of its planning permission by failing to construct an adequate access road to the site. "This minor misunderstanding was rectified immediately it was raised," said the Dart spokesman.

Dart Energy's plans to drill 22 coal-bed methane wells in Scotland are currently being examined by a public enquiry, at which 2500 people have lodged objections. Friends of the Earth Scotland says the industry often resorts to fracking to increase productivity once the gas flow from coal-bed methane wells begins to decline after several years of operation.