A few years ago, the idea of all of London's top-ranked private equity partners being at US firms would have been unimaginable for many in the City.

But Kirkland & Ellis's hire of Freshfields Bruckhaus Deringer Adrian Maguire – just a year after his former magic circle colleague David Higgins made the same move – marks a watershed moment for the City.

Maguire was one of the last of the top-ranking private equity partners practising at a UK firm, according to Chambers and Partners, and now he's Kirkland's man.

Many in the City have expressed shock at Maguire's move, based on his personality and his reputation as a Freshfields man through and through.

Partners describe Maguire as a "team player" and a "really nice guy", but also as someone unlikely to be attracted by the hard-headed, competitive culture of US firms, despite receiving many such offers.

Although several partners across the City said they believed Maguire joined Kirkland on a $10m (£8m) pay package, the actual figure is lower

The fact that even Maguire has moved is likely to make other UK firm stalwarts think twice about where their loyalties lie. As one private equity partner at a US firm points out: "This move will act as a catalyst to make people in magic circle or silver circle firms analyse whether there are better long-term prospects for them in a US firm. This is a starting point for other people to work out their own position."

Although several partners across the City said they believed Maguire joined Kirkland on a $10m (£8m) pay package, the actual figure is lower. People close to the situation described the rise as several million dollars more than what he was on at Freshfields, which insiders say was slightly more than £2m ($2.5m).

Neither is Maguire on a guarantee, which would have secured his earnings for a few years, according to one person familiar with the matter.

But the rise was still something that would almost certainly have been out of reach for Freshfields, as Maguire's colleagues conceded. Even with its revamped system, Freshfields' commitment to a lockstep model means it is unable to pay top earners as much as US firms, which operate an 'eat what you kill' model.

The appeal for Kirkland is also clear. Maguire was co-head of Freshfields' global financial investors group and led Freshfields' highly regarded buyout offering alongside Higgins for many years.

One top private equity partner said: "You can no longer say Kirkland or Latham are not credible."

However, one former Freshfields partner suggested Kirkland's strategy is more nuanced than a simple case of acquiring top talent and a roster of portable clients, and compares the firm's approach to Google and Facebook snapping up startups before they become competitors.

It makes sense to neutralise the competition to protect the franchise. Spending 10 bucks to save $300 – why not?

"US firms tend to be highly strategic," the former partner said. "They're capable of hiring people from a competitor just to destabilise them. If you're Kirkland and you have a global PE business of, say $300m, with five or six key clients, it makes sense to neutralise the competition to protect the franchise. Spending 10 bucks to save $300 – why not?"

Maguire's move also leaves Freshfields' private equity practice in a quandary. One City partner said: "It leaves Freshfields with a relatively young team. Any team that loses its top two rainmakers would see an impact on the practice."

While other rivals say age and experience may not be a problem in itself, questions as to who will pick up key client relationships in Higgins' and Maguire's wake have been raised.

Private equity house Cinven is one such client that may find its attention turned, and while private equity partner Charles Hayes has been picking up much of the CVC work for Freshfields during Maguire's six-month sabbatical, Latham & Watkins won a large mandate for CVC and Blackstone last year on their £2.96bn acquisition of Paysafe Group.

Victoria Sigeti, James Scott and Tim Wilmot have been mentioned as key partners to take the practice forward.

The departures also raise questions about the changes Freshfields made to its lockstep last year, an overhaul that was intended to stem the flow of senior exits but has been followed by a series of high-profile departures, including Higgins and high-yield star Ward McKimm, now at Shearman & Sterling.

Former managing partner Chris Pugh took the fall for the firm's poor financial performance in 2016-17, stepping down as co-managing partner in July 2017, and scrutiny is now likely to turn to senior partner Edward Braham. Three ex-partners suggest it is "inescapable" that Braham will face growing pressure to address what is seen by many as a failed experiment.

Pugh was made to step down for less than this

"The modified lockstep has failed," said one former Freshfields partner. "Pugh was made to step down for less than this. You modify the lockstep not for those establishment players who will never leave like, say, Julian Long, but to make it less likely for those who may want to go, like a Higgins, a McKimm or indeed a Maguire."

The revised lockstep, ushered in for the 2018-19 financial year, enabled the firm to pay top performers about six times more than those at the bottom of the lockstep. Though designed to retain star talent, one former partner said the shake-up had failed. "The two figureheads it was most aimed at [Higgins and Maguire] have walked out the door, so now it's open season."

A Freshfields spokesperson said: "Our lockstep model supports our strategy of delivering high-quality, global advice for our clients, working in effective cross-border teams. It was well debated and supported before it was implemented last year."

So what next for Freshfields' private equity team, once thought of as the City's premier practice? A PE partner at a rival US firm said: "It can go two ways – either people leave over time, like what happened at Linklaters, or they'll lock it down and build up a new practice."

Another City private equity partner added: "Is it the end of Freshfields' PE practice? No. But it seriously dents its offering."

The immediate question for Freshfields is whether more departures will follow. As one private equity partner at a rival firm commented: "There's no point taking just one partner – you have to move other partners as well, so that the balance tips in favour of Kirkland. You'd still say now that Freshfields is a premier player in the market, but a year from now I think we'll see the gap closing."