a) yes. Usually with fixed rates, if you end the contract early, by paying it of or make a change, you have to pay (usually substantially), could even be a couiple of thousand quid. Your paperwork will tell you. You dont really just transefer the debt into someone elses name, the lender has to approve them etc, like when you first got it. Even then, if they are lending the money to a completely different person they wont just trnsfer it. it will be as if you paid off your mortgage with the money they lend him
b)Yes ... they will take into account any debts you have including credit cards, car loans, loans, overdrafts etc, and have access to your credit files so you cant lie. The amount of debt you already have will affect the amount you can afford to repay to them so it will affect the amount they can lend you.
On a seperate note, unless your b/f is very rich, or you are buying a cheap house, can he afford the mortgage on his own?? If its to be a joint house why would you want it all in his name? If you split up, he could chuck you out and you wouldnt get any benefit of any money youd contributed to the house