Whitbread (LSE: WTB) had been a hugely reliable growth play prior to a year ago. In fact, its shares had risen by 285% in the five years from May 2010 to May 2015. However, since then its shares have dropped by almost a quarter as investors have become increasingly concerned about the company’s growth prospects and valuation.

In terms of its growth potential, Whitbread is facing a rather uncertain future. That’s because its cost base is rapidly rising as the living wage causes staff costs to increase and while Whitbread apparently intends to pass such increased costs onto consumers, this could hurt its sales and profitability. Regarding its valuation, Whitbread now trades on a price-to-earnings (P/E) ratio of 15.8 which, given its forecast growth in earnings of 4% for the current year, may appear to be somewhat high.

However, with Whitbread’s earnings growth due to return to a much more encouraging 10% next year, it trades on a price-to-earnings-growth (PEG) ratio of only 1.5. This indicates that while its future is somewhat uncertain, Whitbread has a sufficiently wide margin of safety to merit investment at the present time.

The uncertainty principle

Similarly, the outlook for Berkeley (LSE: BKG) is also uncertain. The UK housing market appears to be expensive compared to historical levels, with the price-to-buyer income ratio being close to its highest-ever level. And with there being the potential for a Brexit next month, Berkeley’s sales could come under pressure as foreign investors look for better value and potentially more security elsewhere.

However, with Berkeley forecast to increase its bottom line by as much as 51% in the current financial year, investor sentiment could rapidly improve in the coming months. That’s especially the case since Berkeley trades on a P/E ratio of just 11.2, which indicates that its shares could deliver a major upward rerating in the medium-to-long term. So, while Berkeley isn’t risk-free, its potential rewards appear to outweigh its risks and this makes it a sound long-term buy.

The diversity dividend

Meanwhile, Mediclinic (LSE: MDC) offers excellent long-term growth prospects, with its operations in Southern Africa and the Middle East in particular having the potential to boost its top and bottom lines. In addition, Mediclinic’s Swiss exposure provides it with additional diversity that could be a useful ally during a period of uncertainty for the world economy.

Looking ahead, Mediclinic is forecast to increase its bottom line by 30% in the current year and by a further 12% next year. This puts it on a PEG ratio of just 0.7 and this shows that while the company’s shares have fallen by 21% since the start of the year, there’s plenty of scope for a reversal of this performance over the medium-to-long term. And with Mediclinic having a beta of just 0.7, it offers a potentially less volatile shareholder experience, too.

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Peter Stephens owns shares of Berkeley Group Holdings. The Motley Fool UK has recommended Berkeley Group Holdings. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.