sadly, you can't easily compare person 1 against person 2 as everything from job to postcode can dramatically change the quote, then add variables like limited mileage, parking location, etc which all mess with the numbers. Plus, that's all before upping the excess to get a better yearly premium - e.g. the Polo guy might have a massive excess while the other might be £150. Then, obviously 1 insurer will happily charge more than other, so the Polo guy might have just done a lot more phoning around to get more quotes and stumbled upon a cheaper deal.
So, the only way you can compare yourself (or 1 person) against another is to be in the exact same postcode, with the same job, etc. which doesn't happen...
Once you've found a car you think is reasonable, then go through the online comparison sites and be creative (without lying) with your job title... e.g. can you try engineer instead of apprentice, then mechanical engineer might give a different result to electrical engineer - all depends your speciality. If you're mechanical engineer apprentice, then could you try mechanic? there's LOADS of options on the drop-downs and they all produce different numbers.
Also remember to add gf and/or parents (possibly better to be your mum) to the insurance as a named driver. I think it's fraudulent for you to be a named driver on their policy if it's your car (as the policy holder is meant to be the main user), but they can be named drivers on your policy (and their experience, assuming they have some no claims, seems to help drop the cost, even if they never use it).