Disposing off interest

Assalaamu Alaikum,
We have 5 partners in the business and I am the only muslim.
I have been allocated around £1000 as my share of the interest received in our work business bank account. I have paid £450 tax on this . So do I donate the £550 to charity (to dispose off impure wealth) or do I donate the entire £1000 ?

If I donate the entire amount of £1000 and I gift aid donation, charity will receive 1250 and I will get back £250 (25% of 1250) through next year’s tax returns. Do I need to give this to charity too ? So in total do I donate 1250 when only £550 of the interest money has come to me after deducting tax ?

I will obviously ask my colleagues and accountant not to allocate any interest money for me from this but wanted to dispose off the money from last accounting year .

JazakAllah khair