The BofE base rate is the same for all banks, but the bank itself generally sets it's own base rate. The APR is the rate that you will be paying (i.e. the extent of interest on your borrowings) however, this will be subject to change throughout the term of the loan (unless you can find a fixed rate for life!). Therefore, in answer to your question, the 5.45% will be the amount of interest added to your borrowings each year.....however, remember this is calculated regularly and you will make payments to "pay off" your debt (if you are capital and interest). Note that as you pay off more, the actual amount of interest you will pay will decrease.....
Hope this helps.