Is it permissible to lie to authorities to obtain government financial aid in Britain on the pretext of high taxes, and is the money resulting from that unlawful (haram), affecting the acceptance of prayers (du'a) and Hajj?

Lying is forbidden (haram), and money obtained through it is illicit (haram) wealth. Consuming what is unlawful may prevent prayers from being accepted, as stated in the Hadith: "His food is unlawful, his drink is unlawful, his clothing is unlawful, and he is nourished by what is unlawful; so how can he be answered?" Performing Hajj with unlawful money renders the Hajj invalid.