Finance balance transfer to credit card?

There are different options - all with benefits and disadvantages.

It is unlikely that Black Horse will accept credit card payments so you would need a money transfer card to transfer the money to your bank account and then pay it off from there. That would allow you to pay it off at 0% for the length of the offer.

Risks are:-
Unless you're a high earner with a good credit history you are unlikely to get £12k as a limit.
There will be a fee. It will vary but could be 3%
Watch minimum payments as they vary for different companies and you will need to meet at least them every month.
The standard rate for the card could be high. Certainly likely to be higher than 11% If you haven't paid off the loan by the end of the 0% period you might not get another transfer at 0% if your circumstances or market conditions have changed. Then you'd be stuck with higher rate.

Personally I'd go for it - try an eligibility checker for the chance of approval and apply for one which has a high chance, but you need to know what you are doing and the risks.

A cheaper loan might be an option if you are eligible. The best rates are around 3% which would be a substantial saving, but you might not get one.

Another option is overpaying. At 11% over 8 years if you overpay £100 now it will save you over £80 in interest. That saving will reduce for subsequent £100s as you reduce the term and it reduces with the passage of time but it will still be very much worth doing.