What a pain it can be to get first time insurance for 17/18 year old kids. I hear horror stories everyday about the massive cost of insuring first time drivers, often only 3rd party and sometimes up to 5 times the value of the car!
However there are some winners; I know some people who finally managed to get insurance for their son who had just turned 17. At first the best quote they got was from the Post Office at £1,500 which when you consider the car (a 99 on a V, 1.0 hatchback) cost £1,000 was, quite simply, ridiculous. Anyway after trawling go compare they finally got the insurance through Quinn Direct* an Irish company, with the mother being the registered keeper and the son being the main driver, fully comp for £460.
You certainly do have to shop around.