Ishi,
I don’t live in the UK, so the educational/professional requirements will vary.
In the US, public and private schools (faith-based schools are private schools) usually require at least a Bachelor’s Degree in Education (takes 4 years to complete). Private schools can be more lenient and will hire teachers who are out of field (have a different degree) but will require you to work toward earning your teacher certification/license…especially if you plan to stick around in teaching. The certification process can include taking teaching courses and passing a certification exam.
Do you know of anyone who teaches at an Islamic school that provide you with information? If not, then why don’t you call your local Islamic school and find out…or pay a visit..talk to the teachers, etc. We live in two different countries, so I can’t help you out much.