been there, done that and worn the t-shirt i'm still paying for.
on an amount as large a 8k is pretty much given you'll not be paying that back in a lump sum or even 12 months.
HMRC will only investigate your incomings/outgoings if you are telling them it'll take you more than 10 years to pay back. If you really cant afford that - tbh its a fair wedge a month for anyone, then they will ask for your month expendeture vs money coming in.
Not sure of your particular financial scenario but a quick calculation tells me a monthly figure of around 70 quid month will take you to just under 10 years.