Yes, you CAN use it in the exam

This is the Casio fx-991ES and it is the calculator I recommend for all my A level students. It is available in WHSmith and Ryman, but the cheapest price is usually on Amazon.

I recommend it for two reasons. First, you can type in mathematical expressions so that they look on the screen like they look on paper. This makes it much easier to use and avoids making mistakes due to misplaced brackets.

Second, it is terrific for checking your answers to questions. For example, it can solve quadratic equations, cubic equations and simultaneous equations; and it can find the value of integrals and derivatives.

However, every year I hear from a student that their teacher has told them that they cannot use it in exams. This is wrong. Calculators that can perform symbolic manipulations are indeed banned in exams, but this calculator cannot do that. It can only, for example, evaluate definite integrals and give you the value of a derivative at a specific point. It only performs numerical calculations. As such it is allowed in the exam.

The official word on this is given in section 3, on page 12, of the Instructions for conducting examinations, published by the Joint Council for Qualifications. These regulations apply to all the English exam boards.