Claiming cleaning allowance from PAYE job, with Self Assesement 2nd ebay side business?

Hello, Can I claim cleaning allowance whilst working for royal mail full time, and having my own "self employed" job selling on ebay? when I go to claim, it asks if i've done a self assessment, which I have, and then goes on to say i need to claim through that. But my self assement part has nothing to do with working for royal mail, and its the royal mail uniform i'm claiming for, I don't wear this when doing my 2nd side little money earner through ebay thanks

Hi,
A Self Assessment tax return is used to declare your worldwide income and capital gains arising in a tax year. In the return you would declare your employment and claim employment expenses such as cleaning your uniform.  
You also declare your self employment income and self employment expenses and any other sources of income. For example, bank building society interest, pensions, benefits, income from property, foreign income, trust income, capital gains income and many more.
Thank you.