Don't go 3rd party or fire & theft as they are more expensive than fully comp now. Try money supermarket or compare the market as they use specialist insurance companies that only deal with people under 25.
No they're not. It depends on the insurer/the risk.
I work in insurance, and the only way to find a good deal is to try different permutations. There's tons of rubbish on the Internet, and it depends how bothered you are about the type of cover versus the cost. The company I work for specialise in bad risks (i.e.: you, I'm afraid!). If you want to, PM me your details (name, contact number, address and date cover required) and I'll forward them to our broker division - they'll give you a quote but won't rip you off with admin fees etc. - e.g.: they'll be a bit more sympathetic as you "know" someone who works for the Group.