Wages from lilah and donations
In the name of Allah, the most Beneficent, the most Merciful.
Maulana Ashraf Ali Thanwi (RA) has said taking a certain percentage from the donations of a madrasah or an Islamic institution for collecting the donation is impermissible. This is known as “Ijarah Majhuul”. (Invalid lease) (Imdadul Fatawa p.376 v.3 & Ahsanul Fatawa p.276 v.7)
Ibn Human (RA) has said ‘Knowledge of the wages or rental must be obtained through explicit specification.’ (Fathul Qadir p.148 & p.178 v.7)
With regards to your final question if there is a need for you to top up your low income with working tax credit then it will be permissible for you take without any detestability. There are many texts found in the books of the jurists and scholars that a needy person can get help and provision from the Baitul Maal (the central treasury of an Islamic state). Therefore, as I mentioned above as long as you are in need and more importantly entitle to it then to get working tax credit or jobseekers allowance will be permissible.
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham.