Can I get full refund if I cancel my British flight 844-873-0997 within 24 hours?

The cancellation policy for them is exactly the same.
Refundable tickets will get refunds.
And non-refundable ones will get travel credits/vouchers.
There is no penalty for canceling these flights.
And you can cancel award tickets anytime as long it adheres to the No show policy, that requires a ticket to be cancelled at least 10 minutes before departure.
The refunded points will go back to your Rapid Rewards account.
Singapore Airways Cancellation Policy for Flights Paid with Companion Pass and Gift Cards