You can threaten to take the "friend" to Court for recovery of the loan. If you did start Court action you would have to pay a Court fee, which would be added to the debt if you won. (Look at HM Courts Service site for details of procedure etc.)
Whether you would win would depend on whether the judge believed you or believed your "friend" - who, I assume, would deny the loan was ever made or would pretend it was a gift.
If you have any evidence at all - eg did you pay by cheque (if so get a copy from your bank); if you paid by cash did you withdraw £1000 from your bank just beforehand (again, get a copy of the transaction document or bank statement) - make sure it is submitted to Court, & also make sure the "friend" knows you have it & will use it if you have to. It may make him/her decide to repay you without the hassle of Court action.
Don't make the mistake of thinking that there is nothing you can do, even if you have no firm evidence. A verbal contract is still a binding contract - the difficulty is in proving it & a lot will depend on the judge's view of your truthfulness & your "friend's" truthfulness.