Last week’s wild swings in crypto-currencies such as Bitcoin jangled investor nerves while the collapse of outsourcing giant Carillion caused anxiety closer to home.

Stock market volatility now looks set to make a comeback in 2018 amid warnings that the second longest bull run in history may finally be coming to an end.

Donald Trump marked his first anniversary as US President yesterday after a bumper year for the nation’s share prices.

The Dow Jones Industrial average index has jumped 32 per cent from 19,800 to more than 26,000 since Trump took office and Ian Heslop, manager of the Old Mutual US Equity Income Fund, said: “The US economy is humming along nicely, and its stock market reflects this.”

The US economy should be given a further lift by Trump’s corporation tax cuts, even though it faces a government lockdown after Congress failed to resolve a bitter row over spending and immigration.

However, others warn that US share prices are hugely expensive after the nine-year bull market that began in March 2009.

The Shiller price-to-earnings ratio shows the S&P 500 trading at 33.86 times company earnings, double its long-term average of 16.82.

It has topped 30 only twice in history, peaking at 32.6 immediately before the 1929 Wall Street crash and 44.2 before the dot.com meltdown in 2000.

Donald Maxwell-Scott, technical investment manager at Rowan Dartington, said markets could be in for a bumpy ride as inflation rises and central bankers increase interest rates and rein in monetary stimulus: “There is no shortage of market commentators predicting we are moments away from the end and financial doom awaits us all.”

Nick Dixon, investment director at insurer Aegon, said markets have raced ahead of economic fundamentals. “The current bull run may have run its course.”

Many are now taking evasive action with Josh Saul, chief executive of The Pure gold Company, reporting a 42 per cent rise in first-time investors buying gold this month: “Fears of a crypto-currency crash, geopolitical tensions and Brexit uncertainty are prompting safe-haven sales.”

He also saw a surge from financial services professionals fearing systemic risk after the failure of Carillion, saying: “They are seeking wealth preservation during uncertain times.”

Others are more bullish, with Lee Wild, head of equity strategy at Interactive Investor, saying news that Chinese GDP rose 6.9 per cent in 2017 removes one potential banana skin.

However, Bitcoin could face a “bloody end” as South Korean and Chinese governments ponder a trading ban.