Polos vary, depending upon the exact model, roughly between Insurance Groups 9 and 23. You can check the exact group here:
http://www.parkers.co.uk/cars/insurance/car-insurance-groups/
So, whatever the result of your check, it's clear that a Polo is nowhere near to the lowest group for insurance purposes.
The age & value of the car probably isn't particularly important anyway (particularly if a 3rd part only, or 3rd party+ fire-&-theft, policy is to be taken out). What the insurance really has to cover is possible multi-million payouts to several people who are all in a car that collides with the Polo, with the Polo driver at fault and the crash victims all suffering life-changing injuries, requiring round-the-clock care for each of them for many decades.
I'd be surprised if
any 17 year old driver can get an insurance quote under £2000, with £3000 being a more likely figure. (However there are other unknowns here, such as the postcode where the driver lives, so it's impossible to offer an accurate estimate).
There are some ways of getting quotes down, which you can read about here:
http://www.moneysavingexpert.com/car-insurance/young-drivers
In particular, adding an experienced 'named driver' (such as a parent) to a policy can see the cost cut by as much as a third. It's irrelevant as to whether the 'named driver' will ever actually drive the vehicle. (That's completely legal. It's doing things the other way round, called 'fronting', where the vehicle is insured by the experienced driver and the novice then added as a 'named driver' which you must most definitely avoid!)