When cooking basmati rice I measure mine in a measuring jug, just like Delia. Only I use 3oz of rice per person. Then double the amount of water, add a little salt, stick a lid on the pan and bring to the boil. When it has boiled turn down to simmer, keeping the lid on (though I usually give a quick stir when it's just boiled), and wait about 12 minutes, or until the rice has absorbed all the water.
When cooking long grain rice I use about a coffee cup of rice per two people, stick in a large pan of boiling, salted water. When rice is cooked drain into a colander and pour a kettle full of boiling water over it.
When making risotto again I use a coffee cup of rice per person.