Hi YYZ,
There are no Income Tax implications on cash gifts from family members, only tax on any interest this accrues from the bank account once transfered.
It appears SA106 box 42 relates to assetts and benefits transfered from abroad, therefore there is no requirement to complete this section as it is a gift of money.
Please check with the Inheritance Tax office with regards to the cash gift as we can only comment regarding Income Tax:
Inheritance Tax: general enquiries
Thank you