'Can you direct us to the Prime Meridian?’ Light was fading on the path winding down from the Observatory and the Americans had left it late for photographs astride the line. But summer evenings are seductive in our oldest Royal Park.

Earlier, in the area behind the Pavilion Café I read my book while a blackbird sang. Squirrels scampered between tables with furled umbrellas and a pair of Magpies stalked the grass.

Passing General Woolf's statue, I admired the view of what’s been called the best architecture in England. Lengthening shadows stretched towards the Palladian elegance of the Queen's House, flanked by colonnades and the Maritime Museum. The domes of Wren’s Naval College beyond were barely visible, but the Thames meandered like a silver ribbon across the city.

Using a flash at the Meridian Line is small price to pay for the atmosphere of Greenwich Park at dusk.