Some mums have been known to lay an extra place for dinner every night for several months. It can take a long time before they develop a new life for themselves. "I think it is like a bereavement for some, and they find it very scary," says Claire Davies, director of studies at private crammer Davies, Laing and Dick.
Others adjust more quickly. "I can remember I was absolutely devastated when my first - a daughter - went off to university," says Hilary McKendrick, mother of three. "She was also devastated. I thought I was going to miss her dreadfully. We dropped her off in Edinburgh and the two girls she was sharing a room with could not have been more friendly. My feelings changed to one of immense jealousy. All the freshers in Edinburgh do a massive pub crawl and people were thumping on her door asking her to go out with them. I was green with envy. Neither of us looked back after that."
Parents of girls find it particularly difficult to let them go compared with boys, particularly mums who haven't had full-time jobs, according to Martin Lloyd, principal of Mander Portman Woodward tutorial college in Birmingham. Some mothers have developed close relationships with their daughters and find the home lacking in fun and intimacy once their girls have left. Fathers want to protect their daughters from drugs, alcohol and predatory males.
Initially parents need to work out how they are going to keep in touch with their offspring, such as how often to ring them. The best thing is to play it cool. Give your child a phone card that lets them ring only your number, and wait. You may find they're homesick and need to call nightly. "The only sane advice is to harden your heart a little, and say: 'Why don't you see how it goes for the next three days and give us a ring then'," says Mr Lloyd. Most students settle in quite quickly.
You may also need to be tough about money. Students are notoriously hard up these days, particularly in London, so most parents are as indulgent as they can afford to be. If you do need to bail out your offspring - and you think they're being a spendthrift - make sure they pay you back by washing the car or hoovering in the vacations. You may find they stop asking you for more.
Children flying the nest can put marriages under strain, particularly if the parents' relationship was largely defined by being mum and dad - prepare yourself for change.