Hi Nin Ping Sunny Paul Suen,
Transferring the interest to another account may prevent the first account (Account A) from becoming a mixed fund, however, you will create a mixed fund account (Account B) that contains the interest accumulated.
You then apply the mixed fund ordering rules covered at RDRM35240 and S809Q of the legislation.
Further guidance in relation to mixed funds rules are at RDRM35210-RDRM35330.
Residence, Domicile and Remittance Basis Manual