It spent the whole morning with us, exploring the garden boundaries, presumably looking for a way out.
It didn't appear to be injured.
After several hours we became concerned that it didn't have enough space, a long enough runway, to be able to fly into the air. I looked up the telephone number for the RSPCA. It was the usual palaver, press one if the animal is stuck in a chimney, press two if.. and so on. I took another look in the garden while I waited to speak to a human
and the swan had gone.