If your landlord doesn't follow the proper guidelines for protecting your deposit, you can sue your landlord for it's return plus deposit x3 compensation. However, if you take your landlord to court and he then protects the deposit and gives you the needed information about the deposit the judge may throw out your claim or find against you so its not a sure thing. You should probably find out if the deposit is protected first. I think you can search with both schemes to see if they're holding your details. If it isn't you can always kindly make your landlord aware of his responcibility in that regard and what you can do if he doesn't protect your deposit. Obviously if you sue or threaten to sue your landlord you're likely to be served with notice to find somewhere else to live so you might want to be sure you want to move out at the end of your fixed term as well.
You can't technically use your deposit to pay your rent, you have an agreement to pay the rent each month. But a lot of landlords are aware that tenants will use the deposit to cover the rent in the last month or two, so it's up to you if you want to do that.