I know a couple of people on the A-Level School Leaver scheme at KPMG and they have been told that they will certify with ATT & CTA (Charted Tax Associate) within 3 years. Once they are certified, they can expect to start at around £35-40k. Salaries don't increase a great deal initially in accountancy like it can at banks, but £40k at the age of 21 struck me!!! I would take the ATT & CTA option if your going to train with the Big4 firms. Also, as a CTA, you can set up a private firm specialising in taxation, for example, inheritance tax or estate planning....these guys charge upto £800 an hour!!! (Some may not believe this but think about it logically. A guy has £15million to give as inheritance to his kids, if there was no tax planning done, he would automatically have to give 40% (upper rate of income tax) i.e. £6million to the HMRC!!!! Suddenly, £10/20/30k in tax planning advice seems insignificant!!!!
Good luck in whatever you do...but bear in mind, even guys from the most prestigious unis e.g. Oxbridge & LSE find it difficult to get jobs at IBs and Big4...a degree is not as valuable as people perhaps think. However, most graduate jobs require a degree and ACA/CTA is no substitute unfortunately. Often they require both!!!