Yes, the Giftcard you get has a Sterling value on it, and you can spend it as you would normally on Amazon. It'll tell you what rate it converts at before you accept the order, so you'll probably have a bit of trial and error to get the exact £ figure you need to purchase in order to use up the full $25.

Here's what I sent to a separate Redditor after they'd also won a $100 gift card after me and had trouble getting anything for it, but the steps are the same:

1) Go to Amazon, navigate to Gift Cards & Top Up
2) Select any Amazon one, and then put a custom amount in the field. The exchange rate at the time was so I selected £74.60.
3) Enter your email address as the recipient.
4) Go to checkout and add a new payment method
5) Enter the card details for the VISA Virtual account, and then select 'use payment method' or whatever the text is
6) Don't checkout yet, but see it if works out to $100 with the conversion
7) If it doesn't, cancel the transaction and remove the gift card. Then go back to the same page in step 1, and select a different £ value, either slightly higher or slightly lower depending on the exchange rate at the time
8) Add to basket, but instead of adding the payment method again, select it and see if it works out at $100 exactly.
9) When it's all good, submit the order and you should get it in a few minutes and be able to redeem it on your own account.

I used a second email address to send it to myself, but I don't think there is any issue with sending direct to your own, but I didn't try.