An understudy never knows when the big day will come

When you have to wait your turn behind a legendary football manager, say, or a vigorous monarch, it can seem that your chance will never come.

One of the toughest jobs in show business is that of the understudy. Just imagine a life in which your sole task is to be on call each and every night, waiting in the wings in case you're required to take over from the incumbent. But 99 times out of 100 your services aren't needed and you can stand down. But then, just as you relax your guard, the call will suddenly come.

The performer you're covering is stuck in traffic, or hurt his back or even (if you're lucky) resigned from the role. Suddenly the gig's yours.

The trouble is, you never know when, or if, the call will come.

For one long-term understudy, the wait is finally over. Following Sir Alex Ferguson's sudden retirement as manager of mighty Manchester United, David Moyes has been appointed as his successor, a job he has long coveted and for which he was believed to have been Sir Alex's preferred candidate.

In truth, Moyes seemed almost as taken aback as the rest of us by the news, for Sir Alex, at 71 and with another Premier League title safely under his belt, seemed capable of going on forever. Yet the great man has pulled off perhaps the hardest trick of his entire career, that of listening to his instinct rather than the blandishments of those who assured him he was immortal.

Now Moyes at last has a chance to show what he can do.

For another high-profile understudy, however, the wait goes on. There must be times when Prince Charles, at 64, wonders if he will ever become king. Until recently, his mother, Queen Elizabeth II, had seemed invincible. Since acceding to the throne in 1952 she has carried out her duties with unwavering dedication for over 60 years: rarely ill, never faltering, and always showing supreme aplomb.

Now, at 87 - an age at which many people can only slump in front of the television with a bag of boiled sweets - she attends nearly 300 public engagements a year.

Yet in the last few weeks there have been signs that she, too, may at last be beginning to wind down. The first indication of her waning powers was the announcement from Buckingham Palace that she will not be attending this year's Commonwealth heads of government conference, scheduled for Sri Lanka in November. Instead, Prince Charles will represent her.

The Queen has only ever missed two such meetings, on both occasions due to her pregnancies.

But long-haul aircraft travel is notoriously wearisome, and the fact that she has ceded this duty to her eldest son this year has been interpreted by royalty-watchers as the first visible indication of the passing of the baton.

There have been other signs. In delivering her speech at the state opening of Parliament last week, Her Majesty seemed for the first time in anyone's memory to be a little less than certain in her delivery. Her address, lasting a little over seven minutes, was uncharacteristically littered with fluffs and stumbles. And was it my imagination, or did her voice seem more frail than usual?

If the Queen did indeed want to step down after 60 glorious years there would be few who'd blame her. Yet the fundamental difference between being monarch and being the manager of a football club is that in the former there is no mechanism in place for a transition of power unless there is a death involved. It is, to all intents and purposes, a job for life.

Yet recent events in the Netherlands, when the much-loved Queen Beatrix ceded power to her son with no more than a wave of a fountain pen, suggests that such a process is easy if all parties are willing to make it happen. The Dutch welcomed their new King Willem-Alexander with enthusiasm, and Charles, too, would be assured of a warm welcome. He is now only seven years younger than Sir Alex, so if he is to fulfil his own destiny, better that it come sooner rather than later.

For Moyes, meanwhile, life could not be sweeter, as he inherits a footballing magic kingdom: rich, powerful, and with a huge international following. When the call comes for Prince Charles to accede to his throne, he may find his job prospects rather more nebulous, and success in the post more difficult to quantify.

Still, there's one advantage he'll have that Moyes will sadly never enjoy. A British monarch is in no danger of being shown the exit if results don't go his way.

Michael Simkins is an actor and writer based in London