A cross-party group of MPs and peers have written to the health secretary requesting an “urgent” meeting to discuss “unregulated” and “untested” treatments that are being offered to long Covid patients in the UK.

It comes after The Independent uncovered a wide range of unproven and “dangerous” therapies being touted to patients, few of which have been approved for use in the NHS – or rigorously tested – for alleviating persistent coronavirus symptoms.

Patients with long Covid are also travelling abroad to clinics in Europe to receive treatments such as “blood washing”, often at a cost of tens of thousands of pounds, according to a report by The BMJ.

In a letter to health secretary Steve Barclay, the All-Party Parliamentary Group on Coronavirus expressed concern that patients “desperately” awaiting treatment through the NHS are being exploited by private clinics, and urged the government to launch an investigation into the provision of unproven care.

The group wrote: “It has come to the attention of the APPG that a number of unregulated long Covid clinics are operating in the UK, offering untested and unscientific treatments to people living with long Covid.

“The evidence our parliamentary group has heard makes it clear that in some parts of the country the current NHS long Covid care pathways are unfit for purpose, with access to NHS long Covid clinics being described as a ‘postcode lottery’.”

Estimates show there are around 807,000 people in the UK who have been suffering from long Covid for more than a year, while 409,000 report that their ability to undertake day-to-day activities has been “limited a lot”.

Approved therapies are provided by the NHS through its long Covid clinics, but these are heavily over-subscribed and only see around 5,000 patients a month.

The APPG continued: “While those living with long Covid desperately await treatment through the NHS, non CQC approved clinics are … exploiting the void of research and care pathways created by the limitations in our understanding of long Covid.”

Among a wide range of unproven therapies provided by private clinics, patients are being recommended probiotic implants, clot-busting drugs which carry the risk of heavy bleeding and haemorrhaging, IV infusions, and “bioresonance” – a holistic therapy that erroneously claims to remove lingering viral matter from the body via electromagnetic waves.

Clinics can charge a high price for such treatments, typically hundreds of pounds, while blood filtering and anti-clotting therapy can cost tens of thousands of pounds. Concerns have also been raised that a number of these therapies could potentially harm patients.

The Advertising Standards Authority (ASA) said it was aware of a rise in clinics claiming to treat long Covid without providing evidence.

The APPG on Coronavirus, which counts Conservative MP Dan Poulter, Green MP Caroline Lucas and the Liberal Democrat’s Layla Moran among its members, urged the government to “urgently launch an investigation into the rise and practices of unregulated long Covid clinics in the UK”.

In their letter, the group adds: “Long Covid is already taking a serious toll on the UK’s health and economy, with a quarter of UK employers citing long Covid as one of the main causes of long-term sickness among staff.

“We cannot risk further harm to those who already seen their lives change so dramatically as a result of Covid-19 infection. Please let me know when you may be available to discuss this pressing issue.”

Mr Poulter, vice-chair of the APPG, said The Independent’s revelations were “a reminder to ministers of the urgent need to fund important research into the long-term impacts of the virus”.

He added: “An investigation must be launched to address these worrying reports and a commitment must be made by the government to dedicate £100m a year in research funding to develop treatments for this condition.”

David Strain, a senior clinical lecturer at Exeter University and long Covid specialist, said patients with long Covid are “absolutely desperate”.

He said: “They want treatments to be here now. What we’re facing is patients who are desperate for any treatments. As things become available, until we have the right evidence base, then people will go and try these therapies. We need to be doing more to support these people.”