The Legal Ombudsman said it is unable to help thousands of people in disputes over unregulated services such as will writing and family law.
The majority of complaints to the ombudsman concerned conveyancing, family law and wills, according to the organisation's first annual report.
Will writing accounted for 13.35% of the cases the ombudsman accepted for investigation.
Residential conveyancing accounted for the greatest majority of cases, with 20.18% of investigated cases being in this area.
Family law was another problem area, accounting for 19.19% of cases.
However, Chief Ombudsman for England and Wales Adam Simpson said that, in a large number of cases, the watchdog could not help people who had dealt with unregulated companies such as will writers instead of solicitors.
He called for action to be taken so consumers are no longer left with no opportunity for redress during disputes with unregulated companies.
"One service which crops up a lot is will writing. It is a service carried out often by will-writing firms who aren't regulated," Sampson told the BBC.
"Because of this, customers are left with little means of redress when things go wrong."
The news comes after the Legal Services Consumer Panel called for will writing services to be regulated after an undercover probe unearthed common poor practice.
The Panel called for a requirement for will writing service providers to prove their competence and follow a code of conduct.
It also recommended the Legal Ombudsman accept cases concerning unregulated will writers.
Will writers already have two trade bodies, the Institute of Professional Will Writers (IPWW) and the Society of Will Writers (SWW).
However, these do not have the power to stop companies from trading in cases of malpractice.
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