If you receive a loan from your parents, it is treated legally just as a loan fom a bank, or from any private person with spare money. You don't pay tax on a loan that you get from your bank (or your parents), and the bank (or your parents) don't pay tax when you repay the loan. If you pay interest, the parents will have to pay tax on the interest, just like they would have to pay tax if the money was in their own bank account.
I would advice both you and your parents to make sure that a contract is signed saying that this is a loan, and how it is repaid, and that you follow the contract. Otherwise, if you or your parents treat the loan as an actual present, then you might have to pay tax, because there is tax due on gifts. And you might get a penalty for trying to avoid tax by declaring the gift as a loan. So pay the money back!
Only up to £3,000 in cash gifts that a person gives each year is tax free, but the parents can use any unused money from last year (so they can give a gift of £6,000 if they gave nothing in the previous year), and it is per parent, so both the mother and father can make a gift.