The lady

It’s a perfect wig,” breathes the publicist solemnly, letting the phrase hang in the air for a moment. We’re high up in the dress circle of the New Wimbledon Theatre. It is January, and dotted throughout the cavernous red-velvet space below us are a director, 40-odd television crew members, and 166 extras in dinner jackets and silk gowns – channelling more 1980s pomp than a mid-Thatcher-era fundraiser. It is exactly the sort of razzamatazz you want from a show rumoured to cost more than $18 million an episode, but beyond the fabulousness, what you really sense is anxiety-level anticipation. We’re all waiting for the wig.

Marilyn Monroe and Alexander the Great aside, there is no rival in the historical blonde stakes to Diana, Princess of Wales, so it took more than a year for The Crown’s producers to settle on the woman who would – who could – carry off her hair’s feathery fulsomeness for series four of the hypnotically soapy and successful royal docudrama. Spanning Diana’s life from age 16 (when she first met Prince Charles, then dating her sister, Lady Sarah Spencer, at a grouse shoot at Althorp) to 28 (when the marriage was in such a desperate state it will make viewers gasp).

Then, after a strung-out 12 months, that she says