An “urgent review” must be taken into the environmental regulator’s actions following complaints about a controversial landfill site, the Welsh government has said.

Residents near the Withyhedge landfill site near Haverfordwest, Pembrokeshire, have previously described it as like “a stink bomb on steroids”.

The site was featured in a Channel 4 Dispatches programme on Friday, which claimed unsuitable waste, including vials of blood, have been dumped at the site.

The company which operates the site has denied unsuitable waste has been placed in landfill and has apologised to residents for the smell.

Wales’ environmental watchdog, National Resources Wales (NRW), said it is working to address the issue.

The firm’s director, David Neal, who has twice been convicted for environmental offences, has been at the centre of a row involving a £200,000 donation from his company to the leadership campaign of First Minister Vaughan Gething.

Mr Neal was given a suspended prison sentence in 2013 for illegally dumping waste on a conservation site and four years later he was prosecuted again for not removing it.

Mr Gething has always maintained the rules over the donations have been followed.

The Channel 4 show claimed the “eggy” smell reported by residents is the result of the chemical hydrogen sulphide.

An anonymous interviewee, who claims to have worked for Mr Neal’s company as a driver for about two years from 2020, said he had witnessed recycling taken to the Withyhedge site for sorting instead be dumped in landfill.

He claimed this included materials such as tyres, syringes and those known to produce hydrogen sulphide, including plasterboard.

Another former worker told the programme that medical waste, sometimes including vials of blood, would come into the site on a “daily basis”.

A third former worker told the programme that leachate – polluted liquid that drains from a landfill – had not been properly disposed of.

They said it was taken from rubbish cells at the site, and placed in holes in the ground.

The programme claimed that leachate can also cause the “eggy” hydrogen sulphide smell, while also causing environmental harm if it leaks into surrounding nature.

On Tuesday, Public Health Wales revealed that its monitoring of the Withyhedge site had detected levels of hydrogen sulphide gas during March and April which at times were above World Health Organisation (WHO) guidelines.

Officials said their advice remained that residents should keep doors and windows closed when the smells are present, and to seek medical advice if they feel unwell.

In a statement, following the Channel 4 programme, a Welsh government spokesperson said: “Natural Resources Wales is responsible for ensuring landfill operators fully comply with strict environmental and legal requirements.

“Given the serious nature of the issues raised by the programme, we have asked NRW to urgently review what action it took to investigate and address the complaints raised directly with it since 2020.”

Andrew RT Davies, Senedd leader of the Welsh Conservatives, said it is “high time” the Welsh government and NRW “rectify this situation which has gone on far too long”.

“The evidence and allegations put forward last night in the Channel 4 programme regarding the first minister’s donor’s company cannot be ignored and urgent action must finally be taken,” he said.

“We know that the owner of the company, that has been creating an unearthly stink at Withyhedge… donated to Vaughan Gething’s leadership campaign to the tune of the largest sum in devolution history.”

Rhun ap Iorwerth, leader of Plaid Cymru, said: “Last night’s programme raises further serious questions about Vaughan Gething’s judgement in accepting a large donation from David Neal, a convicted environmental polluter.

“There are urgent actions that must now be taken regarding the latest evidence revealed by Channel 4’s Dispatches programme.

“We also need to know why it is only now that Welsh government are requesting an urgent review from NRW, when concerns about David Neal’s operations have long been public.”

Responding, Gareth O’Shea of NRW said the regulator has been “gathering information” to determine if further enforcement action is needed.

“Since the odour issues at the site were first identified in late October 2023, our priority has always been to ensure the operator takes the action required to remediate the most likely source of those odours as quickly as possible.

“We have had a significant regulatory presence on site whilst addressing non-compliances linked to the odour issues.

“We will continue to work closely with Pembrokeshire County Council and Public Health Wales to tackle the issues at Withyhedge Landfill… and not stop until the operator at Withyhedge demonstrates that it is effectively managing the odours from its operation.”

The operator of Withyhedge landfill has denied dumping inappropriate materials at the site, apologised to residents for the smell and said it has invested millions of pounds into rectifying the site’s issues.