Will writers and other legal services firms have been slapped with a warning against 'misleading or aggressive' sales practices and threatened with an official probe by the Competition and Markets Authority.

The watchdog issued guidance to seven unidentified firms on how to treat customers fairly, and openly published its letter to unregulated legal providers.

It cautions businesses not to use 'particularly concerning practices' when people are at some of the most challenging times in their lives.

The CMA is trying to stamp out poor behaviour like aggressive upselling, refusing refunds and failing to respond to complaints.

Its warning is aimed at legal businesses including pre-paid probate services - which come with a specific stiff warning explained below - and those providing online divorce as well as will writing.

Will writing services have become a cheap and increasingly popular alternative to high street solicitors.

Some are reputable, adhere to codes of conduct, and have lawyers on the payroll to ensure work is carried out correctly - see the box below on what to check before using one.

The CMA says it wants to protect the growing number of consumers opting for unregulated legal services.

'It is crucial they understand and comply with their consumer protection obligations,' it says. 'People buying these services need to be sure they are getting a fair deal.'

The CMA adds: 'Those who receive a letter should acknowledge it and act on any recommendations to review and revise their contract terms and practices.

'With the CMA set to receive stronger enforcement powers from next spring, if concerns are not addressed, the businesses could face a formal investigation.'

The new Digital Markets, Competition and Consumer Act will allow the CMA to determine whether consumer law has been breached, impose fines, and order firms to pay compensation to customers.

The watchdog has also issued guides for customers on what level of service they should expect from unregulated will writers and divorce service providers, and sources of help if things go wrong.

Meanwhile, probate is the formal process of gaining control of an estate after someone has died.

The CMA says: 'Consumers are cautioned to think carefully before buying pre-paid probate plans as they come with significant consumer protection risks, including that the company could cease trading before the consumer's death.'

And it points to a previous warning to the public on pre-paid probate from the Financial Conduct Authority, which says: 'We strongly advise that you consider carefully whether these products meet your needs and offer value before buying as there are no regulatory protections in place for you.'

Sarah Manuel, head of professional standards at the inheritance industry body STEP, welcomes the CMA's action to protect consumers from poor practice in the will writing and legal services industry.

'We fully support their efforts to caution unregulated providers and introduce stronger enforcement powers. We also welcome advice to the public about what to consider when buying will writing services.'

Manuel warns: 'Anyone can set themselves up as a will writer and bad advice can cause significant distress, leaving grieving families to deal with the financial and emotional consequences.

'We hear all too often from the public and our members about the financial and emotional impact of poor advice from dishonest, unqualified and incompetent will writers.'

She adds that in a STEP survey of members last year, 79 per cent had come across wills with errors and 54 per cent were aware of other firms making false claims, such as avoiding care home fees.

'We remain committed to ensuring that those drafting wills are appropriately qualified.

'STEP sets standards for our members who write wills, trusts and similar legal paperwork through our qualifications, Will Code and other tools.'

Manuel says STEP will continue to push for regulation of the will writing industry alongside high-quality training and greater recognition of specialist qualifications.'

Michael Culver, chair of the Association of Lifetime Lawyers and boss of Culver Law, also welcomes the CMA's move but questions whether it goes far enough.

'While many will writing firms, especially those in the Society of Will Writers, must adhere to similar standards to solicitor firms, others do not.

'These firms often make misleading claims about saving care fees, inheritance tax, and probate fees, with little consumer protection. The new guidance and enhanced enforcement powers are therefore a positive step.'

However, he adds: ' Wills and Lasting Powers of Attorney are crucial legal documents, often made during emotional times or by vulnerable individuals.

'It's time for these services to become a reserved legal activity, as in other jurisdictions, to better protect consumers.

'Additionally, there is no mention of the risks associated with DIY will kits, which can lead to costly legal issues and expose vulnerable people to fraud and abuse.'