For economics you can get away without having studied it at A level. You need maths which you have.
Economics it depends where you are applying. You need to look at Ucas an required points. the best places will be hard and the places with lower aademics you cna get into relatively ok. Look at the UCAS site.
Career propsects again depends what you wnat to do and with what employer. If you went to a top uni and did economics hen you might be able to get into a bank in the city and earn a high salary. You have to be very good though. I'd imagine prospects are only limited by your ability.
Uoir A levels are fine.
For law, then there are no requirements on subjects.
Law tends to be very competitive to get onto A*AA is typical.
Careers prospects again it depends if you are good. If you are then you cna make a steady well paying careers in the city or regions. Its very competitive. theres a further vocational stage called the LPC which a good employer will pay for and a 2 year training contract for which you get a reasonable salary, which jumps by almost 50-100% on qualifying.
If you are very good then you cna make good money which rises every year, but if you are average, then you might not get a training contract and could end up thousands in debt. Grads matter.