Investor activism has been making headlines in the U.S. since the end of the global financial crisis, with the likes of Carl Icahn and Bill Ackman acquiring stakes in a company with the aim of overhauling corporate strategy – and possibly management.

While smaller, troubled firms were first to feel pressure from activists, the targets now often include large multinationals – even ones with strong records of performance, such as Apple (AAPL). And U.K. companies are not immune to the trend. There has been a 170 percent increase in activist investor campaigns in Britain since 2011.

In just the last few months, the likes of Alliance Trust and Rolls-Royce have been affected by shareholders pushing for seats on the board, margin improvements, greater efficiency or even a complete change in strategy. GSK has more recently come under pressure to shake up its structure and senior management team.

There are a handful of factors behind the rise of the activist investor — on both the corporate and investor side of the equation. A long bout of low interest rates, mixed performance from other equity management styles, and past successes have given activists much bigger war chests, not to mention increased partnership from traditional long-only managers. Increased transparency and higher corporate governance standards have also made it easier for activists to gain insight and influence. Regardless of the relative importance of these dynamics, it's clear that activist investors as a category are here to stay and demanding answers quickly.

First off, this isn't necessarily a bad thing. On its own, activism shouldn't be a cause for concern. Most activist engagement is quiet; the high-profile and public battles captured in the press are the exception rather than the rule.

Activist voices can be a positive force in keeping companies accountable and responsive. Their influence can prompt a company to think about a host of important initiatives, from leadership succession to pay transparency or gender diversity.

Rather than putting up walls, companies need to listen to active shareholders and be open to the possibility that their ideas will be in their long-term interests. Yet clearly there is also a balance to strike between listening to outside perspectives and giving in to every demand.

There are short- and long-term implications of this for management teams. First and foremost, examine your own vulnerabilities – if you raised an activist fund, how might you attack your own company?

If these "outside-in" weaknesses are right, take action before someone outside forces the dialog. If they aren't, then be prepared to present a fact-based rebuttal. And be sure that key internal and external partners – lawyers, PR teams, investor relations and bankers – are lined up in support of the strategy and the message.