Gift from overseas family - usage tax question

I am going to receive £X amount from my aunt as a financial gift to help support us with living costs. I want to use half the amount gifted to overpay my mortgage to put me into a lower LTV band, my understanding is that this is not taxable. My question is, if I want to use the other half to top up my current Santander 123 account, will the interest earned be taxed? How is this taxed and calculated if so? Will the CGT allowance be relevant? Another option is topping up my rainy-day account in Premium Bonds. If say I win £100 on the Premium Bonds, is this taxed?

Hi itachil,
There are no Income Tax implications on the receipt of a cash gift unless the cash gift generates interest or dividends.
These would then potentially be subject to tax.  
Further guidance can be found here
Tax on savings interest
Tax on dividends
Thank you.