The Co-op, Direct Line, the AA and the Stobart Group are all looking into providing legal services through the Alternative Business Structures regulations changes – dubbed "Tesco Law" even though, ironically, the superstore chain has yet to enter the market.
The Castle Park team – which stemmed from housing, debt and welfare benefit advice charity Community Advice and Law Service (Cals) – is understood to be the first from the not-for-profit sector.
Regulators granted a special waiver of the separate business rule allowing the move to go ahead. Since then, it has altered the rules and other charities are set to follow.
The firm officially launched on Friday, July 26, and over the longer term wants to plough profits back into the charity to support the on-going delivery of free advice in other areas of social welfare law.
Cals, in Charles Street, offers free legal advice to people with housing, debt and welfare issues who cannot afford to pay for it.
Leading the new law firm are experienced, qualified, solicitors Jusleen Arora and Christine Palmer, who both gained their law degrees at De Montfort University.
Jusleen, who handles the family law cases, said: "Starting Castle Park Solicitors is in some ways really scary because we're in very trying times for so many people – there have been so many changes.
"But on the other side, it's exciting for us. People do have to go somewhere for help and will have to pay for services.
"If we can offer somewhere they can get good-quality advice at competitive costs, we can help them. The fat cat lawyers don't do the sort of work we do."
The 40-year-old started as a secretary at a law firm before enrolling at De Montfort in 1998, studying part-time for four years while holding down a full-time job.
She became fully qualified in 2003, initially working for a private law firm, then spending five years as a locum, the last few waiting for the Castle Park Solicitors project to become reality.
She said: "I do this because I feel I can make a difference to people's lives.
"If I can help one parent stay in contact with their child, then I have helped.
"So many people still don't realise legal aid is no longer available to them.
"We have people on benefits who now cannot afford to get legal advice."
Working alongside her is Christine Palmer, a 61-year-old who gained her law degree in 1990 and has worked for not-for-profit agencies since 1996. She still works two days a week as a debt case worker at the Cals charity but, at Castle Park, is the specialist in employment law cases.
She said: "Castle Park is run as a business separately to the charity.
"We are paid staff but we are paid at a much more moderate level than people in private practices.
"We have an ethical ethos. Unfortunately, we cannot give the service for nothing but we have set our rates very competitively.
"Our aim is to help those people who can no longer get legal aid and simply cannot afford to pay for full private legal services.
"We are also offering people the option of 'unbundling' legal services so they can pay only for the bits they really need."
In April, legal aid was axed or restricted for a range of family law, employment and immigration cases.
One of the ways the firm hopes to help clients is to give them more control over their cases, cutting the costs. Some may even opt to conduct their own cases.
Castle Park also offers fixed fee packages, allowing people to budget up front – a one-hour initial meeting is £96 while a 90-minute full-case assessment costs £180.
The idea for an independent law firm was driven forward by Kathryn Burgess, executive director of Cals, and Glenda Terry, now the practice manager at Castle Lane.
Glenda said: "It has taken a long time and there were a lot of difficulties to overcome.
"I don't think they envisaged an organisation like ours to apply.
"It is a complex area and we are small with limited resources. We have to make sure we fully comply with all the regulations, for example, showing we can monitor our performance."
In September, an immigration lawyer is due to join the practice, whose other member of staff is receptionist Jo Di Caprio.