£100 difference is nothing, you are lucky they even offered that on a right of situation. If you have maintained the bike from scratch you will know exactly how much it is worth. If I was you I wouldn't sell it, I'd keep it. You paid £450 in september and the insurance company are offering £400, you're damn lucky; even after de-value you're still getting a good payout. The insurance, and tax is far cheaper for a motorcycle so I'd suggest you keep it and budget for driving lessons. Don't think about a car just yet - you need to get through your driving test first.