Thanks for your question
If you plan to pay all the loan back - then
1) it will not be treated as a gift
2) There will be no interest to declare to the tax
office on which tax must be paid.
They can set up a written contract - that details what they will loan you - how much will be paid back - and over what period of time - (and whatever interest they wish to charge you) and signed by them and you. And detail any default arrangements should you not make payments on time - or fail to make payments.
As far as the legal aspect is concerned, you should each have an independent witness to sign but I am a UK tax expert - and not a UK law
expert - so you may want to seek further advise on this.
Then they can deposit the money straight into your account - so that should the need arise
1) you have evidence that this was a loan from parents
2) they have evidence that this money was loaned and not gifted
3) they have evidence of the repayments received from you to repay the loan
4) Should they not survive before the full loan is repaid - then this can be collected when the estate is reviewed - to tie up all financial aspects
The only tax implication that will arise, is should you pay the loan back with interest - and then your parents should declare this untaxed interest to the tax office after each 5 April