"This listing is about the future," says James Knight, founder and managing director of Keystone Law, which today (16 November) confirmed that it will become the third law firm to float on the London Stock Exchange (LSE).

The initial public offering (IPO), which will take place on 27 November, has been in the making since early last year, when Knight first began thinking about taking the plunge.

As with the first two UK firms to list – Gateley and Gordon Dadds – Keystone will join LSE's AIM market, becoming Keystone Law Group plc. The move will leave the firm with no debt, lock in senior management and shareholders for up to two years, and fuel its strategy for future growth.

Knight explains: "The public market provides a solid platform for us to move forward within. We have been ambitious, and this kind of stable platform is something we believe will help us grow.

"I think Keystone as a firm and business model is suited to this kind of market, and it will also be a good thing for how we are recognised and perceived by clients and other lawyers."

Keystone, which was founded in 2002, was initially conceived as a 'virtual' law firm, with lawyers working remotely rather than from an expensive, central location. However, in recent years, the firm has opened a string of bases across the UK, as well as in Guernsey and Sydney, Australia. According to its website, key clients include RBS, RSA, Siemens and Virgin Atlantic.

The firm is hoping to raise £15m from the float, based on a placing price of 160p per share, valuing it at £50m. Of the capital raised, £7.4m will be used to pay off shareholder debt relating to private equity firm Root Capital's £3.15m investment in 2014, which the firm received after converting to an alternative business structure in 2013, a move that enabled it to take on external capital.

After these debts and IPO-related costs have been paid, Keystone will be debt-free, and the remaining capital will be ploughed into the business.

"Fundamentally, the IPO doesn't represent any deviation from our existing business model. When you do these things you go around to the institutions and fund managers to gauge appetite and get allocations, and the offering was substantially oversubscribed.

"The reason why investors have been so bullish is because they see the Keystone model as the model for the future – particularly in the mid-market – and wholeheartedly believe in the concept of this very different business model," says Knight.

While Knight is keen to stress that the IPO will not prompt Keystone to diverge from its current strategy, the firm intends to draw on new capital resources to expand its geographic reach, which is currently primarily focused on London and the south of the UK.

The IPO will lock in all existing shareholders and management for a period of one to two years, depending on their roles. And while the firm's 260 lawyers will not be offered share options as part of the float, they will of course be able to buy shares in the firm "in the usual way", according to Knight.

He adds: "Equity in traditional law firms is fraught with politics, risks and a there are great deal of strings attached. It stands for something very different from this, which is much more easy and transparent."