Prof Challis said: "With a desktop computer, the transmitter will be in the tower.
"This might be perhaps 20cms from your leg and the exposure would then be around one per cent of that from a mobile phone.
"However if you put a laptop straight on your lap and are using wi-fi, you could be around 2cms from the transmitter, and receiving comparable exposure to that from a mobile phone.
"Children are much more sensitive than adults to a number of other dangers, such as pollutants like lead and UV radiation, so if there should be a problem with mobiles, then it may be a bigger problem for children.
"Since we advise that children should be discouraged from using mobile phones, we should also discourage children from placing their laptop on their lap when they are using wi-fi.
"In view of public concern, I should like to see some measurements of intensities arising from wi-fi made in schools."